Image capturing apparatus provided with image processor

ABSTRACT

An image capturing apparatus capable of performing a suitable illuminance nonuniformity correction by setting a suitable γ-characteristic every block even in the case that the size of a character image projected on a sensing surface changes according to an image capturing magnification, and capable of extracting a boundary area between a white board portion and a background portion and applying a suitable image processing to this boundary area during the illuminance nonuniformity correction for a picked image, and capable of image capturing a representation such as characters drawn on a white board in such a manner that an obtained image is clear and easy to see by suitably performing an illuminance nonuniformity correction even in the case of color image capturing, and capable of detecting a regularly reflected light with high accuracy and can thereby securely prevent an error of obtaining an image of low quality by image capturing, and capable of preventing an error in flash-image capturing a representation such as characters drawn on a white board under insufficient illumination light and effectively perform an illuminance nonuniformity correction.

This application is based on patent application Nos. 9-12999, 9-13000,9-13001, 9-13002, 9-13003, 9-13004, 9-13005, 9-13006, 9-13019, 9-13020,and 9-13021 filed in Japan, the contents of which is hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

This invention relates to an image capturing apparatus capable ofpicking up a light image of an object by an image pickup device such asCCD (Charge Coupled Device) by photoelectrically converting it into anelectric image and storing it in a storage medium such as a hard diskcard after applying a specified image processing thereto.

There have been known electronic cameras as image capturing apparatus.Electronic cameras have, as compared with conventional cameras whichrecord light images on silver halide film, an advantage of picking upimages of satisfactory quality by suitably applying an image qualityprocessing to the picked up images according to im age capturingpurposes and types of objects since the quality of captured image canfreely be processed. Thus, the digital cameras are used as devices notonly for usual picture taking but also for image capturing images suchas characters and figures drawn on a white board at, e.g., a conferencehall.

In the case that a white board on which characters, figures, etc. aredrawn by an electronic camera, the main purpose of the image capturingis to record a representation represented by characters, figures and thelike on the white board. Accordingly, it is desirable to apply such aγ-correction to the captured image as to enhance the clearness of arepresentation portion (a portion of characters and figures) by making awhite portion (white board portion) white. In this case, since avariation in the character density on the white board and an illuminancenonuniformity are large, it is desirable to correct the illuminancenonuniformity (shading correction) by dividing the captured image into aplurality of blocks in a two-dimensional manner and applying theγ-correction block by block.

Specifically, if the white board is assumed to be illuminated by ceilinglights of the room and sunlight coming through the windows, illuminancenonuniformity occurs due to a nonuniform illumination light. By themultiplying effect of this illuminance nonuniformity and a distributionof incident light amount by the so-called law of Cos⁴ θ according towhich an image at an off-axis object point which is incident on theentrance pupil of the taking lens at an angle ω, a distribution of theoutput of the image pickup devices such as CCDs largely varies alonghorizontal and vertical directions on a sensing surface.

Thus, it is desirable to perform the illuminance nonuniformitycorrection by dividing the picked image into a plurality of blocks in atwo-dimensional manner and by applying the γ-correction according to theilluminance in the block for each block. More preferably, it ispreferable to set a proper γ-characteristic for each block by making theblock size as small as possible in order to avoid the creation of apseudo line at the boundary of the blocks resulting from a sudden changein the γ-characteristic in the case that the γ-characteristic set foreach block largely changes between neighboring blocks.

The γ-characteristic for each block used for the γ-correction performedblock by block can be set using the histogram of level-frequencydistribution of the pixel data included, for example, in the block. Inother words, when an image of characters, figures or the like drawn onthe white board is picked up and a histogram of level-frequencydistribution of pixel data constituting the picked image is generated,the generated histogram of level-frequency distribution is normally atwo-peak distribution histogram having a convex portion corresponding tothe character portion at a dark side and a convex portion correspondingto the white portion (white board) at a bright side. The white level isdetected from the convex portion corresponding to the white portion, andthe γ-characteristic is so set as to convert the pixel data above thiswhite level into pixel data of a predetermined white saturation level.

According to the γ-characteristic setting method using the histogram oflevel-frequency distribution, the set γ-characteristic varies accordingto the number and size of characters included in the block in the casethat the picked image is divided into rectangular blocks. If the blocksize in relation to the character size is improper, a suitableγ-characteristic cannot be obtained. For example, if the block size isconsiderably smaller than a suitable size in relation to the charactersize, the character portion takes up a large area in the block and anarea of the white portion is small. The convex portion corresponding tothe white portion of the histogram of level-frequency distributiongenerated using the pixel data in the block becomes small and it isdifficult to determine the white saturation level based on this convexportion. Conversely, if the block size is considerably larger than thesuitable size, the convex portion corresponding to the white portion ofthe histogram of level-frequency distribution generated using the pixeldata in the block is sufficiently large. However, since the whiteportion takes up a large area in the block, the convex portioncorresponding to the white portion becomes moderately sloped due to theinfluence of the nonuniform illuminance. Thus, it is difficult to stablyset the white saturation level based on this convex portion.

The character size in a field of the viewfinder easily varies accordingto the object distance and the image capturing magnification in picturetaking. However, it is not preferable that the quality of imagesobtained by image capturing the same object considerably changesaccording to the object distance and the image capturing magnification.Accordingly, the block size needs to be set at the specified size inrelation to the character size so that a suitable histogram oflevel-frequency distribution can be obtained.

Further according to the γ-characteristic setting method using thehistogram of level-frequency distribution, the histogram oflevel-frequency distribution of the block including both the white boardportion and the background portion displays a two-peak distributionhaving a convex portion corresponding to the white board portion and aconvex portion corresponding to the background portion in a white area.Thus, there is a likelihood that the white level is erroneously detectedbased on the convex portion corresponding to the background portion.

In the case that the background portion is brighter than the white boardportion, the white level is detected based on the convex portioncorresponding to the background portion and the γ-characteristic is setusing this white level, the pixel data of the white board portion arenot converted into pixel data of specified saturation level (pure white)in monochromatic image capturing. If the γ-correction is performed tointensify the black portion to emphasize the characters, the pixel dataof the white board portion are converted into black in some cases. Thisleads to a disadvantage that the white board portion of the blockincluding the background portion turns black. In the case of a colorimage, if the γ-characteristic for the image of any color components isset as above, a part of color components are completely converted intothose of the black saturation level. Therefore, a chromatic coloringphenomenon occurs in the white board portion.

In the case that the white board is captured together with itsbackground, the image quality is considerably reduced, making the imagehard to be seen if the coloring phenomenon occurs in the white boardportion in a boundary area between the white board portion and thebackground portion during the image processing, namely the illuminancenonuniformity correction. Thus, it is desirable to detect the boundaryarea between the white board portion and the background portion and toproperly perform the image processing in this boundary portion duringthe illuminance nonuniformity correction.

In a known image forming apparatus such as a digital copying machine, animage processing (γ-correction) is applied to an image picked by beingphotoelectrically converted into an electrical signal using aγ-characteristic having a relatively large γ-value (γ-characteristichaving a characteristic similar to a binary processing) in order to makea representation such as characters and/or figures copied on a recordingsheet more clear. This γ-correction is performed as follows in order toreduce the influence of the nonuniform illuminance. As shown in FIG. 71,a picked image G is divided into a plurality of long rectangular blocksB(1), B(2), . . . B(n) along sub-scanning direction. γ-characteristicsγ(1), γ(2), . . . γ(n) are set for the respective blocks based on thehistogram of level-frequency distributions of the pixel data included inthe respective blocks B(r). The γ-correction is applied to the pixeldata in each block B(r) (r=1, 2, . . . n) using the γ-characteristicγ(r) corresponding to this block. By this γ-correction, the whiteportion above a specified level is uniformly converted into an image ofa specified white color, and the character portion (black portion) belowthe specified level is uniformly converted into an image of a specifiedblack color. Accordingly, an image which could have been obtained by abinary processing can be obtained.

Japanese Unexamined Patent Publication No. 6-113139 discloses an imagebinary processing apparatus. This apparatus divides a picked image intoa plurality of partial images; generates a histogram of level-frequencydistribution of pixel data included in the block for each of a selectedpartial image block (object partial image block) and a plurality ofpartial image blocks neighboring the object partial image block; sets athreshold value for the object partial image block by neural networkusing the histogram of level-frequency distribution data; and applies abinary processing to the pixel data in the object partial image blockusing this threshold value.

Since the object distance and the copying magnification aresubstantially constant, the picked image is normally divided by blocksof predetermined size during the γ-correction in the known digitalcopying machine. The binary processing technique disclosed in the abovepublication mainly concerns a binary processing in a copying machine anda facsimile machine. This publication does not disclose any measure todeal with a change in the shape of the histogram of level-frequencydistribution when the character density in the block varies according tothe object distance and image capturing magnification. Accordingly, theilluminance nonuniformity correction may not be performed even if theconventional γ-correction technique is applied to digital cameras.According to this γ-correction technique, the picked image is divided bythe blocks only along sub-scanning direction. Thus, even if thistechnique is applied to a picture image where the illuminancenonuniformity occurs in a two-dimensional manner, it is difficult toeffectively correct the illuminance nonuniformity along main scanningdirection.

On the other hand, according to the binary processing techniquedisclosed in the above publication, a picked image is divided by aplurality of blocks arranged as in a matrix and the binary processing isapplied to the pixel data every block. This technique is effective as amethod for correcting the illuminance nonuniformity of a picture image.However, since the histogram of level-frequency distribution of thepixel data is generated every block and the threshold value of thebinary processing is set by neural network using the histogram oflevel-frequency distribution data, a complicated and cumbersomecalculation is disadvantageously required to set the threshold value. Ifthe block size is set too small, the histogram of level-frequencydistribution of the pixel data is improper and a suitable thresholdvalue cannot be set. Further, since a long time is disadvantageouslyrequired for the calculation due to a huge number of blocks, thereshould be a limit in the number of blocks. Further, a calculation madeto avoid the discontinuity of the image quality resulting from adifference between the processings applied to the blocks using differentγ-characteristics is not easy.

The known digital copying machine and the image binary processingapparatus disclosed in the above publication mainly concern the binaryprocessing performed in the copying machine and the facsimile machine.The background portion image is picked substantially at the same whitelevel as the white portion of a document in view of the construction ofthe apparatus. The aforementioned coloring phenomenon quite seldomoccurs and, accordingly, presents no problem. Thus, a problem of thecoloring phenomenon in the boundary area between the white board portionand the background portion is not considered at all and, hence, there isno indication or disclosure concerning this problem.

In the case that the picked image is a color image comprised of threeprimary color components R (red), G (green), B (blue), theaforementioned illuminance nonuniformity correction needs to be appliedto the image of each color components since the 7-correction needs to beapplied to the image of each color components.

If an object is a white board which is relatively pure white and onwhich black characters are drawn, a histogram of level-frequencydistribution is generated using an image of green components having manyluminance components out of the images of the respective colorcomponents R, G, B constituting a color image as a whole, and the whiteportion (the white board portion) can be detected based on the shape ofthis histogram of level-frequency distribution. The illuminancenonuniformity correction can be performed by using the γ-characteristicset for the image of green components for the γ-correction for theimages of red and blue components.

Specifically, if the histogram of level-frequency distribution isgenerated using the pixel signals of green components, and an inputlevel W is set as a white saturation level of the γ-characteristic basedon this histogram of level-frequency distribution, the pixel signals ofgreen components above the input level W are all converted into thepixel signals of the same saturation level. Since the white board isnearly pure white- and the color components R, G, B of the image of thewhite board portion are substantially at the same level, the pixelsignals of red and blue components above the input level W are allconverted into those of the same saturation level even if the sameγ-characteristic is applied thereto. Thus, the image of the whiteportion having the levels of the color components R, G, B above theinput level W can be uniformly converted into an image of a specifiedwhite color.

However, if the white board has a tint, the color components R, G, B ofthe image of the white board portion are not at the same level. Thus, ifthe γ-characteristic set using the image of green components is appliedto the pixel signals of red and blue components, the level balance ofthe color components R, G, B changes and the tint stands out more.Specifically, if the levels of the respective color components R, G, Bare: D_(R), D_(G), D_(B) (D_(G)>D_(R)>D_(B)), the color components areall converted to the saturation level, i.e., a specified white color ina portion having such color components: W<D_(R), W<D_(G), W<D_(B). Forexample, in a portion having such color components: D_(B)<D_(R)<W,W≧D_(G), only the green components are converted into the saturationlevel and the red and blue components are converted to a specified levellower than the saturation level. Accordingly, the image in this portionis converted to, e.g., the one of a striking yellow green color havingstrong green components. As a result, the illuminance nonuniformitycorrection causes a problem of coloring the white portion.

Generally, the white board is seldom captured in pure white because of avariety of conditions including the color temperature of theillumination light and the smear on the white board. Thus, it isnecessary to perform the illuminance nonuniformity correction whiletaking a measure to prevent the aforementioned problem in color imagecapturing. The known digital copying machine and the image binaryprocessing apparatus disclosed in Japanese Unexamined Patent PublicationNo. 6-113139 mainly concerns a binary processing in a copying machineand/or a facsimile machine, and are premised on that a document image ispicked up in the form of a monochromatic image. They neither disclosenor indicate the illuminance nonuniformity correction technique for acolor image and the problem in the illuminance nonuniformity correctionof the color image.

When characters and/or figures drawn on a white board in a conferencehall are to be captured by an electronic camera provided with a built-inflash, the built-in flash is often automatically fired because only aninsufficient amount of illumination light is normally available, therebyresulting in flash image capturing. If the white board is captured fromfront in such flash image capturing, the flash light is regularlyreflected by the white board and the characters or the like drawn on thewhite board become white by this reflection light, with the result thatan image having a low representation value is obtained by the imagecapturing. Even if the flash is not fired, the characters or the likedrawn on the white board become white by the regularly reflectedillumination light in such an image capturing position where theillumination light such as the ceiling light and sunlight is regularlyreflected by the white board. Thus, this case also leads to a similarreduction in the image quality. If the aforementioned illuminancenonuniformity correction is performed in the image processing, anaccurate histogram of level-frequency distribution cannot be generatedin the block including the regularly reflected light. Therefore, theilluminance nonuniformity correction cannot be effectively performed,and the regularly reflected light adversely affects the blocks which arearound this block, but do not include the regularly reflected light. Asa result, the image quality and the representation value areconsiderably reduced.

In known image forming apparatuses such as digital copying machines, ifillumination light is regularly reflected by a document, the density ofcharacters or the like written on the document is considerably reducedby this regularly reflected light and a document image cannot beaccurately picked up. In order to prevent such a problem, a techniquefor detecting the illumination light regularly reflected by the documentwas developed.

This detection technique is such that the histogram of level-frequencydistribution of pixel signals picked by image pickup devices such asCCDs every line of a sensor is generated and the presence or absence ofthe regularly reflected light is judged based on the shape of thehistogram of level-frequency distribution. More specifically, in thecase that the regularly reflected light is included, the pixels havingreceived the regularly reflected light output the pixel signal ofsaturated level. Accordingly, the presence or absence of the regularlyreflected light is judged by, for example, judging whether the frequencyat the saturation level of the histogram of level-frequency distributionexceeds a specified threshold value.

Since a document is illuminated by an artificial light source under aspecified condition in digital copying machines, the regularly reflectedlight can be satisfactorily detected by the line detection of thesensor. However, with electronic cameras, the illumination condition ofthe illumination light is not constant and an external light such as asunlight is incident on the white board as a spot light and regularlyreflected. Thus, if the detection is made every line as with the knownmethod for detecting the regularly reflected light in the digitalcopying machines, it is difficult to securely detect a spot regularlyreflected light and a sufficiently satisfactory detection accuracycannot be ensured.

The binary processing technique disclosed in Japanese Unexamined PatentPublication No. 6-113139 also mainly concerns a binary processing incopying machines and facsimile machines, and does not at all disclosethe aforementioned problem of the regularly reflected light peculiar tothe image capturing of the digital camera and the method for avoidingsuch a problem.

In the case that a representation such as characters and/or figuresdrawn on a white board is captured in an oblique direction with respectto the white board in, e.g., a conference hall due to a seating positionof an image capture person, a perspective geometric distortion iscreated in a captured image because the representation such ascharacters cannot be entirely in focus. Such a distortion reduces thereadability of the representation. In order to solve this problem, anelectronic camera could be proposed which is able to capture an objectimage while correcting the perspective image distortion created therein,in other words, to perform image capturing while correcting an obliquelycaptured image into a pseudo front image (image seen as if it werecaptured from front).

This electronic camera is such that an image capturing magnification ineach pixel position within a field is calculated using an angle ofinclination of an object with respect to the camera, a focal length ofthe taking lens and an object distance, and that a geometric imagedistortion is corrected by enlarging or reducing a part of the capturedimage based on the image capturing magnifications. For example, in thecase that the white board is captured in an oblique direction from theleft, a partial image at the left side of the center of the field isclose to the camera and a partial image at the right side thereof isaway from the camera. Thus, the obliquely captured image is correctedinto a pseudo front image by reducing the left side image and enlargingthe right side image.

Generally, a white board in a conference hall is hardly illuminated at auniform illuminance and can be seldom captured in a front position.Therefore, an image processing adopting both the illuminancenonuniformity correcting function and the oblique image correctingfunction is applied to an image captured in such a scene.

In this case, if the oblique image correction is performed after theilluminance nonuniformity correction, the number of characters in theblocks (character density of the blocks) varies depending on thepositions of the blocks since the image capturing magnification of theobliquely captured image and the character size differ within the field.Accordingly, the shape of the histogram of level-frequency distributiongenerated for each block largely varies among the blocks. Thus, thewhite level becomes discontinuous due to a difference of theγ-characteristics between neighboring blocks, making it difficult toperform a proper illuminance nonuniformity correction and, depending ona case, leading to the creation of a pseudo line at the boundary of theblocks.

On the other hand, there are some cases where the illuminancenonuniformity correction cannot be properly performed even if theilluminance nonuniformity correction is performed after the obliqueimage correction. Specifically, pixel data are missing in a portion ofan image where the oblique image is corrected by the reductionprocessing, and dummy data are filled in this portion. Accordingly, ifthe histogram of level-frequency distribution of the block including thedummy data is generated during the illuminance nonuniformity correction,the obtained histogram of level-frequency distribution cannot beaccurate because of the presence of the dummy data. This leads to animproper γ-characteristic for the block including the dummy data. Thus,the γ-correction cannot be properly applied to the image in this block,and the white level becomes discontinuous between neighboring blocks,thereby creating a pseudo line at the boundary of the blocks.

For the block including the portion where the pixel data are missing,there is a method for generating the histogram of level-frequencydistribution using only effective pixel data. However, this method has adisadvantage that an effective γ-characteristic cannot be obtained for ablock having a small number of effective pixel data despite acomplicated processing of extracting the pixel data.

The above problem occurs not only in the case of correcting thegeometric distortion of the image obtained by image capturing the objectin the oblique direction, but also in the case of correcting a geometricdistortion resulting from the characteristic of an image pickup opticalsystem.

The binary processing technique disclosed in Japanese Unexamined PatentPublication No. 6-113139 mainly concerns a binary processing in copyingmachines and facsimile machines similar to the known digital copyingmachines. This apparatus is not provided with the oblique imagecorrecting function since a document image is not picked up in anoblique direction because of its construction. Accordingly, thisapparatus does not experience the aforementioned problem arising whenboth the illuminance nonuniformity correction and the oblique imagecorrection are performed. Therefore, this publication neither disclosesnor indicates such a problem.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an image capturingapparatus which has overcome the problems residing in the prior art.

It is another object of the present invention to provide a method forprocessing image data generated by an image pickup device which hasovercome the problems residing in the prior art.

According to an aspect of the present invention, an image capturingapparatus comprising: an image pickup device which photoelectricallypicks up a light image of an object to generate image data including anumber of pixel data; a block setter which sets a plurality of blocksover the number of pixel data; a first γ-characteristic setter whichsets a first γ-characteristic for pixel data at a center position ofeach block based on pixel data included in its block; a secondγ-characteristic setter which sets second γ-characteristics for pixeldata at other positions than the center position of each block based onset first γ-characteristics; and a γ-characteristic corrector whichcorrects pixel data of each block in accordance with the set first andsecond γ-characteristics.

According to another aspect of the present invention, an image capturingapparatus comprising: an image pickup device which photoelectricallypicks up a light image of an object to generate image data including anumber of pixel data; a block setter which sets a plurality of blocksover the number of pixel data; a γ-characteristic setter which sets aγ-characteristic for each block based on pixel data included in itsblock; a γ-characteristic corrector which corrects pixel data of eachblock in accordance with the set γ-characteristic; and an imagegeometric distortion corrector which corrects a geometric distortion ofthe image data having been corrected by the γ-characteristic corrector.

According to another aspect of the present invention, an image capturingapparatus comprising: a taking lens having changeable image capturingmagnifications a detector which detects an image capturing magnificationof the taking lens; an image pickup device which photoelectrically picksup a light image of an object passed through the taking lens to generateimage data including a number of pixel data; a block setter which sets aplurality of blocks over the number of pixel data; a block size setterwhich sets a size of each block based on a detected image capturingmagnification; a γ-characteristic setter which sets a γ-characteristicfor each block; and a γ-characteristic corrector which corrects pixeldata of each block in accordance with the set γ-characteristic.

According to another aspect of the present invention, an image capturingapparatus comprising: an image pickup device which photoelectricallypicks up a light image of an object to generate image data including anumber of pixel data; an image geometric distortion corrector whichcorrects a geometric distortion of the image data; a block setter whichsets a plurality of blocks over the image data having been corrected bythe image geometric distortion corrector; a γ-characteristic setterwhich sets a γ-characteristic for each block based on pixel dataincluded in its block; and a γ-characteristic corrector which correctspixel data of each block in accordance with the set γ-characteristic.

According to another aspect of the present invention, an image capturingapparatus comprising: an image pickup device which photoelectricallypicks up a light image of an object to generate image data including anumber of pixel data; and an image geometric distortion corrector whichcorrects a geometric distortion of the image data by applying areduction processing to a specified portion of the image data, andfilling dummy pixel data in a portion where pixel data is to be lost dueto the reduction processing.

According to another aspect of the present invention, an image capturingapparatus comprising: a color image pickup device whichphotoelectrically picks up a light image of an object to generate imagedata of three primary color components; a white level calculator whichcalculates a white level for an image of each color component based onimage data of its color component; a γ-characteristic setter which setsa γ-characteristic for an image of each color component to convert imagedata of its color component above the calculated corresponding whitelevel to a white saturation level; and a γ-characteristic correctorwhich corrects image data of each color component in accordance with theset γ-characteristic.

According to another aspect of the present invention, an image capturingapparatus comprising: an image pickup device which photoelectricallypicks up a light image of an object to generate image data including anumber of pixel data; a block setter which sets a plurality of blocksover image data generated by the image pickup device; a referencehistogram generator which generates a reference histogram for eachblock, the reference histogram representing a level-frequencydistribution of pixel data included in its block; and a block extractorwhich extracts a boundary block including pixel data of a boundarybetween a main subject image and a background image based on thegenerated reference histogram.

According to another aspect of the present invention, an image capturingapparatus comprising: an image pickup device which photoelectricallypicks up a light image of an object to generate image data including anumber of pixel data; a flash device which emits flash light to theobject; an illuminance nonuniformity corrector which performs anilluminance nonuniformity correction to image data generated by theimage pickup device; and a controller which controls the flash device toprohibits emission of flash light when the illuminance nonuniformitycorrection is designated.

According to another aspect of the present invention, an image capturingapparatus comprising: an image pickup device which photoelectricallypicks up a light image of an object to generate image data including anumber of pixel data; a block setter which sets a plurality of blocksover image data generated by the image pickup device; a referencehistogram generator which generates a reference histogram for eachblock, the reference histogram representing a level-frequencydistribution of pixel data included in its block; a detector whichdetects based on a reference histogram for each block whether its blockhas pixel data in connection with light regularly reflected at a mainsubject; and an operator which performs a specified operation when thereis detected to be a block having pixel data in connection with lightregularly reflected at the main subject.

According to another aspect of the present invention, an image capturingapparatus comprising: an image pickup device which photoelectricallypicks up a light image of an object to generate image data including anumber of pixel data; a taking lens which focuses the light image ontoan image pickup surface of the image pickup device; a distance meterwhich meters a distance to the object; a calculator which calculates adistribution of image capturing magnifications within a specifiedportion of the surface of the object based on a focal length of thetaking lens and an object distance metered by the distance meter; ablock setter which sets a plurality of blocks over image data generatedby the image pickup device, the plurality of blocks respectively havingdifferent sizes in accordance with image capturing magnifications; aγ-characteristic setter which sets a γ-characteristic for each blockbased on pixel data included in its block; a γ-characteristic correctorwhich corrects pixel data of each block in accordance with the setγ-characteristic; and an image geometric distortion corrector whichcorrects, based on a calculated distribution of image capturingmagnifications, a geometric distortion of γ-characteristic correctedimage data that is caused by an oblique image capture.

According to another aspect of the present invention, a method forprocessing image data generated by an image pickup device, the imagedata including a number of pixel data, the method comprising the stepsof setting a plurality of blocks over the number of pixel data; settinga first γ-characteristic for pixel data at a center position of eachblock based on pixel data included in its block; setting secondγ-characteristics for pixel data at other positions than the centerposition of each block based on set first γ-characteristics; andcorrecting pixel data of each block in accordance with the set first andsecond γ-characteristics.

According to another aspect of the present invention, a method forprocessing image data generated by an image pickup device, the imagedata including a number of pixel data, the method comprising the stepsof: setting a plurality of blocks over the number of pixel data; settinga γ-characteristic for each block based on pixel data included in itsblock; correcting pixel data of each block in accordance with the setγ-characteristic; and correcting a geometric distortion of theγ-characteristic corrected image data.

According to another aspect of the present invention, a method forprocessing image data which is generated by an image pickup devicephotoelectrically picking up a light image of an object through a takinglens having changeable image capturing magnifications, the image dataincluding a number of pixel data, the method comprising the steps of:detecting an image capturing magnification of the taking lens; setting aplurality of blocks over the number of pixel data; setting a size ofeach block based on a detected image capturing magnification; setting aγ-characteristic for each block; and correcting pixel data of each blockin accordance with the set γ-characteristic.

According to another aspect of the present invention, a method forprocessing image data generated by an image pickup device, the imagedata including a number of pixel data, the method comprising the stepsof correcting a geometric distortion of the image data; setting aplurality of blocks over the corrected image data; setting aγ-characteristic for each block based on pixel data included in itsblock; and correcting pixel data of each block in accordance with theset γ-characteristic.

According to another aspect of the present invention, a method forprocessing image data generated by an image pickup device, the imagedata including a number of pixel data, the method comprising the stepsof: correcting a geometric distortion of the image data by applying areduction processing to a specified portion of the image data, andfilling dummy pixel data in a portion where pixel data is to be lost dueto the reduction processing.

According to another aspect of the present invention, a method forprocessing image data of three primary color components generated by acolor image pickup device, the method comprising the steps of:calculating a white level for an image of each color component based onimage data of its color component; setting a γ-characteristic for animage of each color component to convert image data of its colorcomponent above the calculated corresponding white level to a whitesaturation level; and correcting image data of each color component inaccordance with the set γ-characteristic.

According to another aspect of the present invention, a method forprocessing image data generated by an image pickup device, the imagedata including a number of pixel data, the method comprising the stepsof: setting a plurality of blocks over image data; generating areference histogram for each block, the reference histogram representinga level-frequency distribution of pixel data included in its block; andextracting a boundary block including pixel data of a boundary between amain subject image and a background image based on the generatedreference histogram.

According to another aspect of the present invention, a method forcontrolling an image capturing apparatus provided with an illuminancenonuniformity corrector for performing an illuminance nonuniformitycorrection to obtained image data, and a flash device for emitting flashlight to an object, the method comprising the step of prohibiting flashlight emission of the flash device when the illuminance nonuniformitycorrection is designated.

According to another aspect of the present invention, a method forprocessing image data generated by an image pickup device, the imagedata including a number of pixel data, the method comprising the stepsof: setting a plurality of blocks over the number of pixel data;generating a reference histogram for each block, the reference histogramrepresenting a level-frequency distribution of pixel data included inits block; detecting based on a reference histogram for each blockwhether its block has pixel data in connection with light regularlyreflected at a main subject; and performing a specified operation whenthere is detected to be a block having pixel data in connection withlight regularly reflected at the main subject.

According to another aspect of the present invention, a method forprocessing image data which is generated by an image pickup devicephotoelectrically picking up a light image of an object through a takinglens having a focal length, the image data including a number of pixeldata, the method comprising the steps of: metering a distance to anobject; calculating a distribution of image capturing magnificationswithin a specified portion of a surface of the object based on a focallength of the taking lens and a metered object distance; setting aplurality of blocks over the number of pixel data, the plurality ofblocks respectively having different sizes in accordance with imagecapturing magnifications; setting a γ-characteristic for each blockbased on pixel data included in its block; correcting pixel data of eachblock in accordance with the set γ-characteristic; and correcting, basedon a calculated distribution of image capturing magnifications, ageometric distortion of γ-characteristic corrected image data that iscaused by an oblique image capture.

These and other objects, features and advantages of the presentinvention will become more apparent upon a reading of the followingdetailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing an external configuration of anelectronic camera according to a first embodiment of the invention;

FIG. 2 is a rear view of the electronic camera;

FIG. 3 is a perspective view showing oblique image capturing of anobject;

FIGS. 4A and 4B are diagrams showing the oblique image capturing,wherein FIG. 4A shows an obliquely captured image and FIG. 4B shows animage after an oblique image correction;

FIG. 5 is a perspective view showing an example of illuminatingdirections of illumination light for a white board;

FIGS. 6A and 6B are graphs showing distributions of output of an imagepickup device, wherein FIG. 6A shows an output distribution alongvertical direction and

FIG. 6B shows an output distribution along horizontal direction;

FIG. 7 is a diagram showing a schematic construction of an opticalsystem of the electronic camera of the first embodiment;

FIG. 8 is a diagram showing an image sensing system in oblique imagecapturing when viewed from above;

FIG. 9 is a diagram showing a sensed image divided into a plurality ofblocks;

FIG. 10 is a graph showing an exemplary γ-characteristic forintensifying a white portion set for each block;

FIG. 11 is a graph showing an exemplary γ-characteristic forintensifying a black portion;

FIG. 12 is a graph showing a relationship between a black adjustment bya black density adjustment switch and a γ-characteristic forintensifying the black portion;

FIG. 13 is a block diagram showing a construction of the electroniccamera of the first embodiment;

FIG. 14 is a block diagram showing a construction of a portion forapplying an image processing to a color image from an oblique imagecorrection device to first and second γ-correction devices;

FIG. 15 is a block diagram showing an internal construction of a firstγ-characteristic setting device;

FIGS. 16A and 16B are diagrams showing the oblique image capturing,wherein FIG. 16A shows an obliquely captured image and FIG. 16B shows animage after the oblique image correction;

FIG. 17 is a diagram showing an image after a portion of pixel datamissed during a compression processing is corrected;

FIG. 18 is a diagram showing the capacity of an image memory;

FIG. 19 is a graph showing a general shape of a histogram oflevel-frequency distribution of pixel data constituting a characterimage;

FIG. 20 is a diagram showing a sensed image divided into a plurality ofsmall images in blocks;

FIGS. 21A and 21B are diagrams showing states where a picked image isdivided by blocks of improper size, wherein FIG. 21A shows a case wherethe block size is smaller than a proper one and FIG. 21B shows a casewhere the block size is larger than the proper one;

FIG. 22 is a diagram showing a viewfinder frame displaying a blockframe;

FIG. 23 is a graph showing an exemplary histogram of level-frequencydistribution of pixel data constituting a small image divided by theblock;

FIG. 24 is a graph showing an exemplary γ-characteristic set using thehistogram of level-frequency distribution of the pixel data;

FIG. 25 is a graph showing an exemplary γ-characteristic set using thepixel data of green components;

FIGS. 26A to 26C are graphs showing γ-characteristics set for therespective color components using the pixel data of the respective colorcomponents, wherein FIG. 26A shows a γ-characteristic for the pixel dataof red components, FIG. 26B shows a γ-characteristic for the pixel dataof green components, and FIG. 26C shows a γ-characteristic for the pixeldata of blue components;

FIG. 27 is a diagram showing an interpolation calculation of theγ-characteristic for the pixel data within an area enclosed by thecenter positions of neighboring blocks;

FIGS. 28 to 30 are flowcharts showing an image capturing control of theelectronic camera according to the first embodiment;

FIG. 31 is a flowchart showing a subroutine “Data Effective AreaCalculation”;

FIG. 32 is a flowchart showing a subroutine “γ-characteristic Setting”;

FIG. 33 is a diagram showing a reading direction of the pixel data ofthe CCD;

FIGS. 34A and 34B are diagrams showing an oblique image correctingmethod, wherein FIG. 34A shows an oblique image and FIG. 34B shows apseudo front image after the oblique image correction;

FIGS. 35A and 35B are diagrams showing an interpolation processing ofthe pixel data in the oblique image correction, wherein FIG. 35A showsthe interpolation processing along vertical direction and FIG. 35B showsthe interpolation processing along horizontal direction;

FIG. 36 is a block diagram showing a construction of an electroniccamera according to a second embodiment of the invention;

FIG. 37 is a block diagram showing an arrangement of an A/D converter tofirst and second γ-correction devices of the electronic camera of thesecond embodiment;

FIG. 38 is a block diagram showing an internal construction of a firstγ-characteristic setting device of the electronic camera according tothe second embodiment;

FIGS. 39A and 39B are diagrams showing an obliquely captured imagedivided into a plurality of small images, wherein FIG. 39A shows theimage divided by blocks of the same size and FIG. 39B shows the imagedivided by blocks of different sizes;

FIGS. 40 to 42 are flowcharts showing an image capturing control of theelectronic camera according to the second embodiment;

FIG. 43 is a flowchart showing a subroutine “Block Size Setting”;

FIG. 44 is a diagram showing a method for setting a γ-characteristic forthe illuminance nonuniformity correction for other blocks using aγ-characteristic for the illuminance nonuniformity correction set forthe blocks arranged along row direction;

FIG. 45 is a diagram showing a method for setting a γ-characteristic forthe illuminance nonuniformity correction for other blocks using aγ-characteristic for the illuminance nonuniformity correction set forthe blocks arranged along column direction;

FIG. 46 is a diagram showing another method for dividing a picked imageby blocks to perform the illuminance nonuniformity correction;

FIG. 47 is a diagram showing blocks including a boundary line between awhite board image and a background image;

FIG. 48 is a graph showing an exemplary histogram of level-frequencydistribution generated for the block including the white board image andthe background image;

FIGS. 49A to 49C are graphs showing the reason why coloring phenomenonoccurs during the γ-correction for the illuminance nonuniformitycorrection and the black intensification, wherein FIG. 49A shows ahistogram of level-frequency distribution, FIG. 49B shows aγ-characteristic for the illuminance nonuniformity correction and FIG.49C shows a γ-characteristic for the black intensification;

FIG. 50 are graphs showing the reason why coloring does not occur duringthe γ-correction for the illuminance nonuniformity correction and theblack intensification, wherein FIG. 50A shows a histogram oflevel-frequency distribution, FIG. 50B shows a γ-characteristic for theilluminance nonuniformity correction and FIG. 50C shows aγ-characteristic for the black intensification;

FIG. 51 is a block diagram showing an internal construction of the firstγ-characteristic setting device for reducing the occurrence of thecoloring phenomenon during the illuminance nonuniformity correction andthe black intensification;

FIG. 52 is a flowchart showing a control “Block Extraction” forextracting the blocks including the background image;

FIG. 53 is a diagram showing a search range for detecting the blocks notincluding the background image around the block including the backgroundimage;

FIGS. 54A to 54D are diagrams showing a search procedure of the blocksnot including the background image, wherein FIG. 54A shows a searchprocedure of the blocks in an upper left area of the block including thebackground image, FIG. 54B shows a search procedure of the blocks in anupper right area of the block including the background image, FIG. 54Cshows a search procedure of the blocks in a lower left area of the blockincluding the background image, and FIG. 54D shows a search procedure ofthe blocks in a lower right area of the block including the backgroundimage;

FIG. 55 is a diagram showing a method for detecting the blocks includingthe boundary between the white board image and the background image;

FIG. 56 is a graph showing an exemplary histogram of level-frequencydistribution generated for the blocks including the white board imageand the background image;

FIG. 57 is a graph showing an exemplary histogram of level-frequencydistribution generated for the block including only an image ofintermediate gradation such as a picture;

FIGS. 58A and 58B are graphs showing a method for expanding a dynamicrange in the γ-correction during the illuminance nonuniformitycorrection, wherein FIG. 58A shows a histogram of level-frequencydistribution and FIG. 58B shows a γ-characteristic;

FIG. 59 is a block diagram showing a construction of an electroniccamera according to a third embodiment of the invention;

FIG. 60 is a block diagram showing a construction of an arrangement ofan A/D converter to first and second γ-correction devices of theelectronic camera of the third embodiment;

FIG. 61 is a block diagram showing an internal construction of a firstγ-characteristic setting device of green components of the electroniccamera according to the third embodiment;

FIG. 62 is a rear view of the electronic camera of the third embodiment;

FIG. 63 is a diagram showing an LED device for warning a regularlyreflected light in a viewfinder;

FIG. 64 is a graph showing a histogram of level-frequency distributionof pixel data of a block including an image represented by regularlyreflected light;

FIGS. 65 to 67 are flowcharts showing an image capturing control of theelectronic camera according to the third embodiment;

FIG. 68 is a flowchart showing a subroutine “Regularly Reflected LightDetection”;

FIG. 69 is a flowchart showing a modification for prohibiting thestorage of the picked image in a hard disk card when the regularlyreflected light is detected;

FIG. 70 is a flowchart showing a modification for forcibly switching aγ-correction to be applied to the picked image to a usual γ-correctionwhen the regularly reflected light is detected; and

FIG. 71 is a diagram showing a method for dividing an image picked in adigital copying machine by blocks.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 is a perspective view showing an external configuration of anelectronic camera according to a first embodiment of the invention, andFIG. 2 is a rear view of this electronic camera.

A camera 1 of FIGS. 1 and 2 includes a CCD area sensor as an imagepickup device. An image data sensed by this CCD area sensor is recordedin an unillustrated hard disk card of PCMCIA standards. Although a casewhere the area sensor is used as an image pickup device is described inthis embodiment, an image data may be picked by scanning an object lightimage by a line sensor.

The camera 1 is provided with a function of correcting an image of anobject whose surface is not parallel with the sensing surface of the CCDarea sensor (hereinafter, “oblique image”) into an image of an objectwhose surface is parallel with the sensing surface of the CCD areasensor (hereinafter, “front image”). Hereinafter, the above correctionis referred to as an oblique image capturing correction.

For example, in the case that characters, figures and the like drawn ona white board 20 are captured in a normal image capturing mode in aposition (A) obliquely forward of the white board 20 to the left asshown in FIG. 3, the captured image is an oblique image K in which adimension at the right end is smaller than that at the left end as shownin FIG. 4A resulting from a different object distance distributionwithin a field. However, the oblique image K is corrected into a frontimage K′ as shown in FIG. 4B which could be obtained by image capturingthe object in a position (B) substantially in front of the white board20.

The electronic camera 1 is also provided with a function of correctingan illuminance nonuniformity, which results from the nonuniformity ofillumination light (ceiling lights, sunlight coming through the windows,etc.) of the white board and a variation of the sensitivity of the CCDarea sensor, for the picked image of the representation (hereinafter,this kind of binary representation is referred to as characterrepresentation) represented by characters, figures and the like drawn onthe white board.

If the white board 20 is illuminated, for example, by the ceiling lightsof the room and the sunlight coming through the windows as shown in FIG.5, illuminance nonuniformity occurs due to the nonuniform illuminationlight. Further, by the multiplying effect of this illuminancenonuniformity and a distribution of incident light amount by theso-called law of Cos⁴ θ according to which an image at an off-axisobject point which is incident on the entrance pupil of the taking lensat an angle ω, a distribution of the output of the CCD area sensorlargely varies along horizontal and vertical directions on a sensingsurface. When the illuminance nonuniformity correction processing isperformed, a proper γ-characteristic is set for each pixel data or foreach pixel data group including a plurality of pixel data. Thetwo-dimensional variation of the output of the CCD area sensor isreduced as much as possible by applying a γ-correction for each pixeldata or for each pixel data group using the γ-characteristic settherefor. In FIGS. 6A and 6B, solid line represents output distributionsof the white portion of the white board 20 when nothing is drawnthereon, whereas dotted line represents output distribution of thecharacter portion when characters are drawn on the white board 20.

The electronic camera 1 according to the first embodiment performs theilluminance nonuniformity correction after performing an oblique imagecorrection as described later.

Here, the principle of oblique image capturing correction is brieflydescribed. It should be noted that description be made on a linear imagein order to simplify the description.

FIG. 7 is a schematic construction diagram of an optical system of thecamera 1. This optical system is such that a laterally long rectangularshaped CCD area sensor 22 (hereinafter, “CCD 22”) is arranged in a focusposition of a taking lens 2 and a diaphragm 21 is arranged between thetaking lens 2 and the CCD 22. A light image representing figures or thelike drawn on the white board 20 is focused on the sensing surface ofthe CCD 22 after having passed through the taking lens 2 and thediaphragm 21.

FIG. 8 is a diagram of an image pickup system viewed from right aboveduring oblique image capturing, wherein the display surface of the whiteboard 20 (hereinafter, “object surface”) is inclined by an angle θ(hereinafter, “angle of inclination O”) with respect to the sensingsurface of the CCD 22.

In FIG. 8, indicated at L is an optic axis of the taking lens 2, and byN0, N1, N2 are line segments parallel to the sensing surface of the CCD22 which pass points P, F, G on the white board 20, respectively. Points0, Q, R, D and E are an intersection of a lens surface of the takinglens 2 and the optic axis L; an intersection of the line segment N1 andthe optic axis L; an intersection of the line segment N2 and the opticaxis L; an intersection of the line segment N0 and the extension of aline segment BF; and an intersection of the line segment N0 and a linesegment GC.

A light image of line segment FG on the white board 20 is formed betweenpoints B and C of the sensing surface of the CCD 22. However, since thesensing surface and the object surface are inclined to each other by theangle of inclination θ, the light image BC formed on the sensing surfaceof the CCD 22 is equivalent to the projection of an image between pointsD and E on the sensing surface of the CCD 22. Assuming that, at therespective points A, B, C on the sensing surface of the CCD 22, imagecapturing magnifications are m_(A), m_(B), m_(C) and object distancesare D_(A)(=OP), D_(B)(=OQ), D_(C)(=OR),m_(B)=m_(A)·OP/OQ=m_(A)˜D_(A)/D_(B),m_(C)=m_(A)·OP/OR=m_(A)·D_(A)/D_(C). Accordingly, m_(B)>m_(A)>m_(C). Thelight image formed on the sensing surface is an oblique image K as shownin FIG. 4A, and only point A (intersection of the optic axis L and thesensing surface) is perfectly in focus among the light image BC.

In this embodiment, the oblique image correction is performed byobtaining an image capturing magnification mi (i=1, 2, . . . n) of therespective points between points A and C on the sensing surface of theCCD 22 and an image capturing magnification mi′ (i′=1, 2, . . . n) ofthe respective points between points B and A on the sensing surface ofthe CCD 22, enlarging the picked image of the light image AC based onthe image capturing magnification mi, and reducing the picked image ofthe light image BA based on the image capturing magnification mi′.

If Di′ is an object distance at an arbitrary point between points B andA on the sensing surface of the CCD 22 and αi is an angle of view atthat point (an angle between a line segment passing that point and thepoint 0 and the optic axis L), D_(A)/Di′=1+tan(αi)·tan(θ). Accordingly,the image capturing magnification mi′ at this arbitrary point can becalculated based on the angle of inclination θ, the image capturingmagnification m_(A) and the angle of view αi in accordance with Equation(1): $\begin{matrix}\begin{matrix}{{mi}^{\prime} = {m_{A} \cdot {D_{A}/{Di}^{\prime}}}} \\{= {m_{A} \cdot \left\{ {1 + {{\tan\left( {\alpha\quad i} \right)} \cdot {\tan(\theta)}}} \right\}}}\end{matrix} & (1)\end{matrix}$

In accordance with Equation (1), the image capturing magnification m_(A)can be calculated as: m_(A)=a·f/D_(A) (where a: proportion coefficient,f: focal length). Further, Equation: D_(A)/Di′=1+tan(αi)·tan (θ) can beobtained as follows, using the object distance D_(B) and the angle ofview α_(B) with respect to point B in FIG. 8:OQ=OP−PQ=OP−OQ·tan(α_(B))·tan(θ)(PQ=FQ·tan(θ),FQ=OQ·tan(α_(B)))∴OP=OQ·{1+tan(α_(B))·tan(θ)}∴D _(A) /D_(B)=1+tan(α_(B))·tan(θ)

Hence, in a position of the arbitrary angle of view a i:D _(A) /Di′=1+tan(αi)tan(θ).

If Di is an object distance at an arbitrary point between points A and Con the sensing surface of the CCD 22 and βi is an angle of view at thatpoint, D_(A)/Di=1−tan(βi)·tan(θ). Accordingly, the image capturingmagnification mi at this arbitrary point can be calculated based on theangle of inclination θ, the image capturing magnification m_(A) and theangle of view βi in accordance with Equation (2): $\begin{matrix}\begin{matrix}{{mi} = {m_{A} \cdot {D_{A}/{Di}}}} \\{= {m_{A} \cdot \left\lbrack {1 + {{\tan\left( {\beta\quad i} \right)} \cdot {\tan(\theta)}}} \right\rbrack}}\end{matrix} & (2)\end{matrix}$

It should be noted that D_(A)/Di′=1−tan(βi)·tan(θ) can be obtainedaccording to the similar method as above.

Next, the illuminance nonuniformity correction is briefly described.

The main purpose of the image obtained by image capturing a characterrepresentation is to record the representation. Such an image isrequired to have an image quality of high representation readabilityrather than depiction. Accordingly, it is desirable to make thecharacter representation clear by making the contrast of the characterrepresentation portion against the white portion of the white board andto make the entire image easily visible by reducing the illuminancenonuniformity.

In this embodiment, as shown in FIG. 9, the picked image G is dividedalong horizontal and vertical directions into a plurality of squareblocks B(I) (I=, 2, . . . 18 in FIG. 9). A γ-characteristic as shown inFIG. 10 is set as a γ-characteristic γ(I) for a center position O(I) ofthe block B(I) based on the white level W calculated using the histogramof level-frequency distribution of the pixel data included in each blockB(I). Further, the γ-characteristics γ(P) of the pixel positions of eachblock B(I) except the center position 0(I) are interpolated. Using theγ-characteristics γ(I), γ(P), γ-correction is applied to the pixel datain the pixel positions O(I), P to make the character representationclear and perform the illuminance nonuniformity correction.

The γ-characteristic of FIG. 10 is the one for a case where the pixeldata are A/D converted into 8-bit data, and “255” is a maximum value ofinput/output levels. With the γ-characteristic shown in FIG. 10, allpixel data above the input level W are converted into the pixel datasaturated to the maximum level. Accordingly, the picked image iscorrected such that the white portion constituted by the pixel dataabove the input level W uniformly becomes white of maximum brightness.In this way, the contrast of the character representation portionagainst the white portion is intensified, making the characterrepresentation clear.

Further, if necessary, γ-correction is applied to the image after theilluminance nonuniformity correction using the γ-characteristic as shownin FIG. 11 to intensify the black portion of the characterrepresentation portion. Specifically, the image after the illuminancenonuniformity correction is corrected such that the black portionconstituted by the pixel data below an input level B uniformly becomesblack of minimum brightness. Accordingly, the blackness of the characterportion is intensified according to the density, the thickness and theline density of the characters, figures and the like drawn on the whiteboard 20 so as to properly make the character representation clear. Theγ-correction in the illuminance nonuniformity correction is described indetail later.

Referring back to FIG. 1, the electronic camera 1 is providedsubstantially in the middle of its front surface with the taking lens 2including a zoom lens, and a light emitting window 4 and a lightreceiving window 5 for metering an object distance by the activemetering system are provided above the taking lens 2. Between thewindows 4 and 5 is provided a light meter window 3 for metering anobject brightness. Further, an objective window 6 of a viewfinder isprovided at the left side of the light emitting window 4 and a flash 7is provided at the right side of the light receiving window 5.

The light emitting window 4 is a window through which infrared rays areprojected toward an object, and the light receiving window 5 is a windowthrough which the infrared rays reflected by the object are received.Although the active metering system is adopted in this embodiment, thepassive metering system may be adopted.

In one side surface of the electronic camera 1 is provided a cardinsertion slot 8 through which a hard disk card 13 (hereinafter, “HDcard 13”) is mounted and ejected. Above the card insertion slot 8 isprovided a card eject button 9 which is operated to eject the HD card13. In the case that the image capturing result is to be printed, the HDcard 13 is ejected from the electronic camera 1 by pushing the cardeject button 9, and is mounted in a printer compatible with the HD card13 for the printout.

It should be appreciated that the electronic camera 1 may be providedwith an interface of SCSI cable and directly connected with a printervia the SCSI cable, so that the image data can be transferred from theelectronic camera 1 to the printer to print the captured images.

Although the hard disk card of PCMCIA standards is adopted as a storagemedium of the image data in this embodiment, any other storage mediumsuch as a memory card and a mini-disk (MD) may be used provided it canstore the captured result as an image data.

On the upper surface of the electronic camera 1 are provided a shutterrelease button 10 at a left end, and a zoom switch 11 and an imagecapturing/reproduction switch 12 at a right end. When the shutterrelease button 10 is partly pressed to turn on an ST1 switch fordesignating the image capturing preparation such as focusing and settingof exposure control values. When the shutter release button 10 is fullypressed to turn on an ST2 switch for designating an exposure. The zoomswitch 11 is a three-contact switch slidable along transverse direction.The zooming ratio of the taking lens 2 can be continuously changed to atelephoto side when the zoom switch 11 is slid toward T(TELE)-side,while being changed to a wide-angle side when the zoom switch 11 is slidtoward W(WIDE)-side.

The image capturing/reproduction switch 12 is a switch for switchinglysetting an image capturing mode and a reproduction mode. The switch 12is a two-contact switch slidable along transverse direction. The imagecapturing of an object (recording of the picked image in the HD card 13)is enabled when the switch 12 is set at an image capturing (REC) side,whereas the display of the picked image stored in the HD card 13 on anLCD device 19 (see FIG. 2) is enabled when the switch 12 is set at areproduction (PLAY) side.

In the rear surface of the electronic camera 1 are provided a mainswitch 14 for electrically activating the camera 1 and an eyepiecewindow 15 of the viewfinder which are located at the left end andsubstantially in the middle of an upper portion, respectively as shownin FIG. 2. At the right side of the eyepiece window 15 is provided amode setting switch 16.

The mode setting switch 16 is operated to switchingly set a usual imagecapturing mode and an oblique image correction mode for correcting anoblique image into a pseudo front image, and has a function of settingthe angle of inclination θ (see FIG. 8).

The mode setting switch 16 includes a transversely long guide groove 16b having an angle scale 16 a on its upper portion, and an operationbutton 16 c movable along the guide groove 16 b. The angle ofinclination θ can be set by setting the operation button 16 c in aspecified angle position of the angle scale 16 a.

In the angle scale 16 a, 0° is arranged in the middle, and 15°, 30° and45° are arranged on each of the opposite sides of 0° so that threedifferent angles of inclination θ can be set on the left and rightsides. Here, the angles on the left side are angles of inclinations inthe case that an object is captured from the left side (hereinafter,“left side oblique image capturing”), whereas the angles on the rightside are angles of inclinations in the case that an object is capturedfrom the right side (hereinafter, “right side oblique image capturing”).If the operation button 16 c is set in the middle position, the angle ofinclination is 0°. Accordingly, the normal image capturing mode is setin which the oblique image capturing correction is not applied to thecaptured image.

Although the angle of inclination θ which an image capture personmeasures by the eye can discretely be set in this embodiment, it maycontinuously be set according to a slide amount of the operation button16 c.

Further, in this embodiment, the angle of inclination θ is measured bythe eye. However, it may be appreciated to measure distances to twoseparate portions of an object from the electronic camera, and calculatean angle of inclination θ based on measured two distances.

Furthermore, an illuminance nonuniformity correction switch 17 and ablack density adjustment switch 18 are provided below the main switch14. Further, the LCD device 19 is provided below the eyepiece window 15.

The illuminance nonuniformity correction switch 17 is a switch fordesignating the aforementioned illuminance nonuniformity correction. Theswitch 17 is an ON/OFF switch whose operation button is slidable alongtransverse direction. When the illuminance nonuniformity correction isdesignated by the switch 17, the picked image is divided into aplurality of blocks (small images), and γ-correction is applied to eachblock using a γ-characteristic as shown in FIG. 10 set using the pixeldata included in the block. On the other hand, when the switch 17 isoff, γ-correction is applied to the picked image using a presetγ-characteristic suitable for usual picture taking (γ-characteristicwhich provides an image of high depiction in which the gradation of anobject can be reproduced as true as possible).

The illuminance nonuniformity correction is designed to improve theimage quality degraded by nonuniform illuminance when image capturingthe character representation drawn on the white board, and is mainlyapplied when image capturing such a character representation.Accordingly, if the content of the captured images is classified intotwo types: “character image” obtained by image capturing arepresentation such as characters and figures and “natural image”obtained by image capturing a landscape or people, the illuminancenonuniformity correction switch 17 serves as a switch for switching theimage processing to the picked image (particularly γ-correction) betweena character image mode and a natural image mode.

When image capturing characters, figures or the like, an image captureperson can obtain a picked image of the quality suitable for a characterimage (representation such as characters is properly emphasized bymaking a white portion whiter) by setting the illuminance nonuniformitycorrection switch 17 “on”. When image capturing a landscape, people orthe like, he can obtain a picked image of the quality suitable for anatural image (high depiction) by setting the illuminance nonuniformitycorrection switch 17 “off”.

The black density adjustment switch 18 is a switch for adjusting theblack saturation level B (see FIG. 11) of the γ-characteristic for theγ-correction for the black intensification to the image after theilluminance nonuniformity correction. The switch 18 is a three-contactswitch whose operation button is slidable along transverse direction.The switch 18 functions only when the illuminance nonuniformitycorrection switch 17 is on (when the character image mode is set). Inthe character mode, the black saturation level of the γ-characteristicis set at a predetermined specified level B0 when the switch 18 is offin the character image mode; it is set at a specified level B1 (>B0)higher than the level B0 when the switch 18 is set at “DARK”; and it isset at a specified level B2 (<B0) lower than the level B0 when theswitch 18 is set at “LIGHT”.

The white saturation level of the γ-characteristic is automaticallyadjusted to make the base portion whiter during the image processing inthe character image mode. However, the density of the character portioncan be changed by changing the black saturation level by the blackdensity adjustment switch 18, thereby adjusting the contrast of thecharacter portion against the base portion (white portion).

For example, if characters drawn on a white board and characters drawnor printed on a document are compared, the characters on the white boardare generally larger and thicker than those on the document.Accordingly, if a γ-correction similar to the one applied when a whiteboard image is picked up is applied when a document image is picked up,the contrast of the characters against the base in the document image isreduced than in the white board image. Thus, in the case that thedocument image is picked up, the blackness of the character portion isintensified by setting the black density adjustment switch 18 at “DARK”,thereby suitably adjusting the contrast of the character portion againstthe base portion.

Although the black saturation level is switched in two stages in thisembodiment, it may be switched in a multitude of stages or may becontinuously changed.

The LCD device 19 is adapted to display the picked image. When the imagecapturing/reproduction switch 12 is set at the reproduction side, thepicked image of the frame designated by an unillustrated selectionswitch is read from the HD card 13 and reproduced and displayed on theLCD device 19.

FIG. 13 is a block construction diagram of the electronic camera 1according to the first embodiment.

In FIG. 13, the same elements as those described above are indicated atthe same reference numerals. A CCD driver 31 controls the image pickupoperation of the CCD 22 based on the shutter speed of the exposurecontrol values inputted from the CPU 30. The CCD 22 include a color areasensor, and is adapted to perform the image pickup operation (electriccharge storing operation) in accordance with a control signal inputtedfrom the CCD driver 31 and to output the pixel signals of the respectivecolor components R, G, B to an image processor 32 after converting theminto signals in time series.

The image processor 32 is adapted to output the pixel signals outputtedfrom the CCD 22 to the HD card 13 after applying a specified signalprocessing thereto. The image processor 32 includes an A/D converter320, an oblique image correction device 321, a data effective areacalculator 322, an image memory 323, first and second γ-characteristicsetting devices 324, 325, first and second γ-correction devices 326,327, and a switch circuit 328, and applies the oblique image correctionto an oblique image. When the illuminance nonuniformity correction isdesignated, the image processor 32 sets a γ-characteristic for theilluminance nonuniformity correction for each block and performs theγ-correction using the set γ-characteristics. At this time, theγ-characteristics corresponding to the positions between the centerpositions of the respective blocks are interpolated. By applying theγ-correction to the pixel signals in these positions using theinterpolated γ-characteristics, the discontinuity of the image qualitycaused by the difference of the γ-characteristics between the blocks canbe moderated.

The A/D converter 320 converts the respective pixel signals included inthe image signal read from the CCD 22 into digital signals (hereinafter,“pixel data”).

The oblique image correction device 321 performs the oblique imagecorrection when the oblique image correction mode is set. The obliqueimage correction device 321 applies enlargement and reductionprocessings along horizontal direction (x-axis direction in FIG. 3) andalong vertical direction (y-axis direction in FIG. 3) based on theaforementioned principle of the oblique image correction.

FIGS. 16A and 16B are diagrams showing an image processing method forcorrecting the captured oblique image into a pseudo front image, whereinFIG. 16A shows an image before the correction and FIG. 16B shows animage after the correction.

In FIG. 16, xy-coordinate systems are orthogonal coordinate systemstentatively provided for an image G picked up by the CCD 22 (imageconstructed by pixel data), and its origin is set in the center of theimage G. An obliquely captured image K included in an image G(corresponding to the white board 20) is an image to which the obliqueimage correction is applied (hereinafter, “correction image”).

Since the focus adjustment position of the camera 1 is set in the centerof the field (origin 0 of the xy-coordinate systems) in this embodiment,a portion of the correction image K on y-axis is accurately in focus inFIG. 16A. An image K1 on the left side of y-axis is an image inclinedtoward the camera 1, whereas an image K2 on the right side of y-axis isan image inclined away from the camera 1.

Accordingly, as shown in FIG. 16B, the image G1 of the image G on theleft side of y-axis is reduced with respect to both x- and y-axes so asto obtain an image G1′. In this way, the trapezoidal oblique image K1 iscorrected into a rectangular reduced image K1′. The image G2 on theright side of y-axis is enlarged with respect to both x- and y-axes toobtain an image G2′. In this way, a trapezoidal oblique image K1 iscorrected into a rectangular enlarged image K2′.

Enlargement and reduction processings of the picked image during theoblique image correction are performed according to the method disclosedin, e.g., Japanese Unexamined Patent Publication No. 8-164722.Specifically, since the object surface is not inclined with respect tothe sensing surface of the CCD 22 along the y-axis direction, aprocessing for correcting the picked image into an image enlarged at amagnification k(>1) is performed by replacing the respective pixel dataconstituting the picked image (image before the correction) by therespective pixel data constituting the picked image which could beobtained by picking up an image obtained by enlarging the original imageat the magnification k.

The enlargement and reduction of the image with respect to the x-axisdirection can be performed based on the same concept of the enlargementand reduction of the image with respect to the y-axis direction.However, since the image capturing magnifications mi, mi′ vary alongx-axis direction and the magnification k differs every pixel, the imageis enlarged and reduced using the magnification ki of each pixel.

In the case of enlargement processing, the magnification ki in anarbitrary pixel position between points A and C in FIG. 8 is expressedas a product of an inverse of a ratio of the image capturingmagnification mi in this pixel position to the image capturingmagnification m_(A) at point A (m_(A)/mi) and a correction coefficient(1/cos(θ)) for correcting an oblique image into a front image, i.e.,ki=(m_(A)/mi)/cos(θ). On the other hand, sincemi/m_(A)=1−tan(βi)·tan(θ)=cos(βi+θ)/(cos(βi)·cos(θ)) from Equation (2),the enlargement magnification ki is calculated by following Equations(3), (4): $\begin{matrix}{{ki} = {1/\left\lbrack {\left\{ {1 - {{\tan\left( {\beta\quad i} \right)} \cdot {\tan(\theta)}}} \right\} \cdot {\cos(\theta)}} \right\rbrack}} & (3) \\{\quad{= {{\cos\left( {\beta\quad i} \right)}/{\cos\left( {{\beta\quad i} + \theta} \right)}}}} & (4)\end{matrix}$

In the case of reduction processing, the reduction magnification ki′ inan arbitrary pixel position between points B and A in FIG. 8 isexpressed as a product of an inverse of a ratio of the image capturingmagnification mi′ in a pixel position to the image capturingmagnification mA at point A (m_(A)/mi′) and the correction coefficient(1/cos(θ)) for correcting an oblique image into a front image, i.e.,ki′=(m_(A)/mi′)/cos(θ). On the other hand, sincemi′/m_(A)=tan(αi)·tan(θ)=cos(αi−θ)/(cos(βi)·cos(θ)) from Equation (1),the reduction magnification ki′ is calculated by following Equations(5), (6): $\begin{matrix}{{ki}^{\prime} = {1/\left\lbrack {\left\{ {1 + {{\tan\left( {\alpha\quad i} \right)} \cdot {\tan(\theta)}}} \right\} \cdot {\cos(\theta)}} \right\rbrack}} & (5) \\{\quad{= {{\cos\left( {\alpha\quad i} \right)}/{\cos\left( {{\alpha\quad i} - \theta} \right)}}}} & (6)\end{matrix}$

Although the obliquely captured image is corrected by the enlargementand reduction processings as described above in this embodiment, it maybe corrected by a so-called pixel addition method according to which animage is enlarged by adding known pixel data to the pixel data and by aso-called pixel weed-out method according to which pixel data are weededout. Further, although the obliquely captured image is corrected by theenlargement and reduction processings, it may be corrected only byeither the enlargement or reduction processing.

If the image G1 is reduced, a portion missing pixel data (see a hatchedarea ΔG1 of FIG. 16B) is seen in the image after the correction. Thecorrected image looks unnatural when being reproduced in a monitortelevision or by a printer. In the example of FIG. 16B, since the pixeldata of noise level are outputted in the portion of the imagecorresponding to the area ΔG1, the quality of this portion becomesunstable during the reproduction, with the result that the image as awhole does not look nice. Thus, during the correction, a white dummydata may be set as, e.g., pixel data so that the missing portion turnswhite.

Since the area ΔG1 has a wedge shape at its upper and lower portions,thereby looking unnatural, a margin area ΔGO comprised of strip-likeareas capable of covering the area ΔG1 may be preferably provided at aleft side portion, an upper side portion and a lower side portion (or aperipheral portion if necessary) of the corrected image G′ as shown inFIG. 17, and a dummy data of a specific color such as white may be setfor the margin area ΔGO. Since such an arrangement makes the reproducedimage rimmed, a sense of unnaturalness can be reduced.

When the usual image capturing mode is set, no correction processing isperformed in the oblique image correction device 321 and the pixel datainputted from the A/D converter 320 are outputted to the image memory323 as they are.

The data effective area calculator 322 calculates an area of the imageafter the oblique image correction except the dummy data (area exceptΔG1 in FIG. 16B, area except ΔG0 in FIG. 17, hereinafter, “dataeffective area”). When a γ-characteristic for the illuminancenonuniformity correction is set for each block after the oblique imageis corrected into a front image, an accurate γ-characteristic cannot beobtained in the blocks including the dummy data because of the presenceof the dummy data. Accordingly, in this embodiment, a γ-characteristicis set using only the effective pixel data excluding the dummy data forsuch blocks as described later. The information on the data effectivearea are calculated by the data effective area calculator 323 is usedwhen the effective pixel data in the respective blocks are extracted.

The image memory 323 is adapted to store the pixel data outputted fromthe oblique image correction device 321. The image memory 323 has acapacity for storing the pixel data corresponding to one frame of pickedimage, so that the image processing can be applied to the entire pickedimage at once.

The capacity of the image memory 323 may be so set as to allow the imageprocessing line by line of the block when the picked image is dividedinto blocks. Specifically, the capacity of the image memory 323 is suchas to store the pixel data included at least in the blocks arrangedalong one row when the picked image is divided into a plurality ofblocks of the maximum settable size. By doing so, the memory capacitycan be reduced. Specifically, if the picked image G is divided, forexample, into 3×3 blocks B(1) to B(9) as shown in FIG. 18, the capacityof the image memory 323 may be so as to store the pixel data included inthe blocks B(1) to B(3), the blocks B(4) to B(6), or the blocks B(7) toB(9) arranged in each row.

The first γ-characteristic setting device 324 is adapted to setγ-characteristics for the illuminance nonuniformity correction of thepicked image. The first γ-characteristic setting device 324 divides thepicked image into a plurality of blocks and sets a γcharacteristic forthe illuminance nonuniformity correction every block using the pixeldata included in each block. The second γ-characteristic setting device325 is adapted to set a γ-characteristic for the black intensificationof the image after the illuminance nonuniformity correction. The secondγ-characteristic setting device 325 sets the γ-characteristic for theblack intensification based on the information on the state of the blackdensity adjustment switch 18 which is inputted from the CPU 30.

The first γ-correction device 326 is a circuit for applying aγ-correction to a natural image, whereas the second γ-correction device327 is a circuit for applying a γ-correction to a character image. Thefirst γ-correction device 326 applies the γ-correction to the pixel dataread from the image memory 323 using a predetermined γ-characteristicsuitable for the natural images. The second γ-correction device 327divides a picked character image into a plurality of blocks, and appliesthe γ-correction to the pixel data constituting the picked image usingthe γ-characteristic for the black intensification set by the secondγ-characteristic setting device 325 after applying the γ-correction tothe pixel data using the γ-characteristics for the illuminancenonuniformity correction set for the respective blocks by the firstγ-characteristic setting device 324. It should be noted that theγ-correction to be applied to the character image is described later.

The switch circuit 328 switches the connection of the image memory 323with the first and second γ-correction devices 326, 327. The switchingof the switch circuit 328 is controllably performed in accordance with acontrol signal outputted from the CPU 30 in correspondence with the setstate of the illuminance nonuniformity correction switch 17. When theilluminance nonuniformity correction switch 17 is off (when the naturalimage mode is set), the image memory 323 is connected with the firstγ-correction device 326. On the other hand, when the illuminancenonuniformity correction switch 17 is on (when the character image modeis set), the image memory 323 is connected with the second γ-correctiondevice 327.

Here, a method for applying the γ-correction (illuminance nonuniformitycorrection and black intensification) to the character image isdescribed.

As described above, it is desirable to make the character portion moreclear than the white portion in the case of the character image. Inorder to make the white portion whiter, a γ-characteristic having anoutput level saturated at a specified input level W as shown in FIG. 10is used.

A histogram of level-frequency distribution of the pixel data of, e.g.,green components constituting the character image is generated, and alevel having a maximum frequency within a range corresponding to thewhite portion is set as a white saturation level W of thisγ-characteristic. In other words, if the histogram of level-frequencydistribution of the pixel data of green components is generated for animage obtained by image capturing the white board 20 on whichcharacters, figures or the like are drawn, it is generally a two-peakdistribution portion having a convex portion U corresponding to a whiteportion (board portion) and a convex portion C corresponding to a blackportion (character portion) as shown in FIG. 19. A level w correspondingto the peak of the convex portion U is set as the white saturation levelW of the γ-characteristic.

The γ-characteristic for determining the white saturation level W may beset based on the histogram of level-frequency distribution of the pixeldata of green components constituting the entire picked image and theγ-correction may be applied to the entire picked image using thischaracteristic. However, the characters drawn on the white board 20 byhand has a largely varying character density (a ratio of the characterportion to the white portion), and a distribution of illuminance largelyvaries within the field in the case of a picture taking since a lightsource is not constant as in a copying machine provided with anilluminating device. Accordingly, it is preferable to correct theilluminance nonuniformity by dividing the picked image into a pluralityof blocks and applying the γ-correction to each block using theγ-characteristic set for each block.

In the electronic camera 1 according to this embodiment, as shown inFIG. 20, the picked image G is divided into n (=K (column)×L (row))blocks B(I, J) (I=1, 2, . . . K, J=1, 2, . . . L) along column and rowdirections, and the γ-characteristic for the illuminance nonuniformitycorrection representing the block B(I, J) is set for each block B(I, J).In this case, the size (area) of the blocks B(I, J) is set such thatabout 9 (3×3) characters can be included therein. The size of the blocksB(I, J) is set in relation to the number of characters for the followingreason. In the case that the histogram of level-frequency distributionis generated using the pixel data in the block, the convex portion Ucorresponding to the white board 20 is permitted to have a suitablysteep slope, so that the peak position w of the convex portion U can besecurely detected.

Specifically, if the block size is set relatively small with respect tothe characters as shown in FIG. 21A, an area of the block B(I, J) takenup by the character portion is large, thereby making the convex portionU of the histogram of level-frequency distribution corresponding to thewhite board 20 flat. Thus, the peak position w of the convex portion Umay be erroneously detected. If the block size is set relatively largewith respect to the characters as shown in FIG. 21B, illuminance largelyvaries in the blocks B(I, J), making the convex portion U of thehistogram of level-frequency distribution corresponding to the whiteboard 20 moderately sloped. In this case as well, the peak position w ofthe convex portion U may be erroneously detected.

In order to determine the block size, it is necessary to know the sizeof the character image projected on the field. The size y′ of thecharacter image projected on the field can be calculated from the size yof the characters drawn on the white board 20 and the image capturingmagnification m: y′=y·m. Further, the size y of the characters drawn onthe white board 20 is considered to be in a specific range although itmay differ depending upon who draws. Accordingly, if a representativevalue y0 of the size y of the characters drawn on the white board 20 andan image capturing magnification m0 are empirically determined, the sizey′ of the character image projected on the field can be simplydetermined from the image capturing magnification m.

In this embodiment, a reference block size S0 is determined based on thesize y0 of the characters projected on the field at the image capturingmagnification m0, the block size S at any arbitrary image capturingmagnification m is calculated based on the image capturing magnificationm0 and the block size S0: S=S0·m/m0. Accordingly, if (i×j) pixel dataare assumed to be included in the block of the size S0, the number i′ ofthe pixel data along column direction of the block of the size S isi·m/m0, and the number j′ of the pixel data along row direction of theblock of the size S is j·m/m0.

Although the block size S is set such that 9 characters are included inthe block in this embodiment, this is only an example. If therepresentative value y0 of the size y of the characters drawn on thewhite board 20 is changed, the number of the characters in the blockchanges. Thus, the block size S is set according to the representativevalue y0 such that a suitable number of characters are included in theblock.

Further, although the block size S is changed according to the imagecapturing magnification m in this embodiment, the image capturingmagnification m may be adjusted to a specified value m0 corresponding tothe block size S0 in image capturing a character image while the blocksize S0 is fixed. Specifically, as shown in FIG. 22, a block frame 43corresponding to the block size S0 may be displayed in the viewfinderframe 42 and an image capture person may adjust the zooming ratio of thetaking lens 2 or the object distance such that an image corresponding to9 characters drawn on the white board 20 falls within this block frame43. The block frame 43 may be displayed constantly or only when thecharacter image is set.

Next, a method for determining the γ-characteristic for the illuminancenonuniformity correction based on the histogram of level-frequencydistribution of the pixel data of green components is described.

Out of (i×j) pixel data g(1, 1), g(1, 2), . . . g(i-1, j), g(i, j)included in the block B(I, J), a predetermined X(%) of pixel data aredeleted from the maximum level toward the lower level. The histogram oflevel-frequency distribution is generated using the remaining pixeldata. For example, if the total number of the pixel data included in theblock is 10000 and X=3%, 300 pixel data added from the maximum level ptoward the lower level are deleted, and the histogram of level-frequencydistribution is generated using the remaining 9700 pixel data. X % ofthe pixel data at the high level side are deleted in order to avoidadverse influences such as a noise.

This histogram of level-frequency distribution is generally a two-peakdistribution histogram as shown in FIG. 23. A convex portion U at thehigh level side corresponds to the base portion of the white board 20,and a convex portion C at the low level corresponds to the characterportion. A level p in FIG. 23 is a maximum level of the pixel dataincluded in the block B(I, J), and a level q (<p) is a maximum level ofthe histogram of level-frequency distribution.

Upon the generation of the histogram of level-frequency distribution, amost frequent level w in a distribution of a predetermined range dextending from the maximum level p toward the low level is calculated,and is set as the white saturation level W of the γ-characteristic forthe illuminance nonuniformity correction. The range d is such that onlythe convex portion U of the high level side is presumed to be securelyincluded in the block captured at a normal illuminance since the blocksize is set at a specified size in relation to the number of characters.If, for example, the pixel data is an 8-bit data and has 0 to 255gradation levels, the width of the range d is set at about 48 levels.

Accordingly, if the maximum level q is, for example, 200, the level whaving a maximum frequency in the level range 152 to 200 is calculated.If the level w is 180, the white saturation level W is set at 180 and aγ-characteristic as shown in FIG. 24 is determined.

In the oblique image correction mode, there is an area where dummy dataexist in a portion of the image to which the compression processing isapplied. If the white saturation level W is set for the block includingthe dummy data using the histogram of level-frequency distribution ofall pixel data including the dummy data, the correct white saturationlevel W cannot be set. Accordingly, for the block including the dummydata, the histogram of level-frequency distribution is generated usingthe effective pixel data excluding the dummy data and the whitesaturation level W is set using this histogram of level-frequencydistribution.

If the white board 20 is not completely white, but slightly colored, orif the white balance adjustment of the electronic camera 1 is improper,the γ-characteristic for the illuminance nonuniformity correction setusing the pixel data of green components cannot be applied for theγ-correction applied to the pixel data of red and blue components sincea γ-value of an equivalent γ-characteristic for the γ-correctionperformed using the γ-characteristic for the illuminance nonuniformitycorrection and the γ-characteristic for the black intensification isrelatively large.

Specifically, let it be assumed that a captured image of a certain areaof the white board 20 is not completely white and levels D_(R), D_(G),D_(B) of the pixel data of the respective color components R, G, B are,for example. (D_(R), D_(G), D_(B)) (130, 140, 125), and aγ-characteristic equivalent to the γ-characteristic for the illuminancenonuniformity correction and the γ-characteristic for the blackintensification which are set using the pixel data of green components(γ-characteristic obtained by combining the two γ-characteristics) isset, for example, as shown in FIG. 25. If the γ-correction is applied tothe pixel data of red and blue components using this γ-characteristic,the outputs of the respective color components are: (DR, DG, DB)=(185,255, 140) as shown in FIG. 25, with the result that the image after theγ-correction turns considerable yellow green.

If the γ-value of the γ-characteristic shown in FIG. 25 is small(moderately sloped), the resulting color difference is almost no problemsince the outputs of the respective color components after theγ-correction differ to a small degree. However, the γ-characteristicused in the character image mode is adapted to perform a γ-correctionsimilar to a binary processing and the γ-value is set relatively large.Accordingly, it is difficult to use the γ-characteristic set using thepixel data of green components for the γ-correction to be applied to thepixel data of red and blue components.

As a method for avoiding the above coloring phenomenon of the whiteportion, there can be considered a method according to which the pixeldata of the color components R, G, B are converted into luminance dataand color difference data and are reconverted into the pixel data of thecolor components R, G, B after the γ-correction is performed using onlythe luminance data. However, according to this method, the colordifference data are kept. Thus, if the characters drawn on the whiteboard 20 are, for example, scratchy light characters, they remain lighteven after the γ-correction. It is difficult to clearly reproduce thelight characters.

In this embodiment, exclusive γ-characteristics for the respective colorcomponents are set by correcting the γ-characteristic for theilluminance nonuniformity correction set using the pixel data of greencomponents. By performing the γ-correction using the exclusiveγ-characteristic for each color component, even the light characters canbe clearly reproduced.

The γ-characteristics for the respective color components are set usingthe pixel data of the respective color components so that an input level(D_(R)-5, D_(G)-5, D_(B)-5) becomes the white saturation level assuminga margin value of the level is “5”. For example, in the example of theγ-characteristic shown in FIG. 25, the γ-characteristics for the colorcomponents R, G, B are set so that the input level of the respectivecolor components R, G, B (125, 135, 120) becomes the white saturationlevel 255 as shown in FIGS. 26A to 26C.

Since the γ-correction is performed so as to make the colored whiteportion white, the color portion has a different color than its originalone. However, it is more important in the character image to reproducethe representation than to reproduce the colors. Thus, the colordifference of a certain degree is thought to be permissible.

In the above description, the histogram of level-frequency distributionof the pixel data included in the block is generated and the whitesaturation level W is determined (i.e., the γ-characteristic is set)based on this histogram of level-frequency distribution. However,instead of using the histogram of level-frequency distribution, theγ-characteristic may be set by calculating the pixel data.

If the γ-characteristic for the illuminance nonuniformity correction isset for each block B(I, J) according to the aforementioned method andthe γ-correction is applied to the image block by block using theseγ-characteristics, the image quality suddenly changes at the boundariesof the blocks since the γ-characteristic for the illuminancenonuniformity correction differs every block. This may create boundarylines (pseudo lines). In other words, the white level suddenly changesat the boundaries of the blocks and this discontinuity of the whitelevel may turn out as boundary lines.

Accordingly, in this embodiment, the γ-characteristic for theilluminance nonuniformity correction set for each block B(I, J) is theγ-characteristic of the pixel data in the center position of the blockB(I, J). γ-characteristics for the illuminance nonuniformity correctionof the pixel data between the center positions of the neighboring blocksare linearly interpolated using the γ-characteristics for theilluminance nonuniformity correction of the two blocks. By applying theγ-correction to the pixel data in positions other than the centerpositions using the linearly interpolated γ-characteristics, thediscontinuity of the image quality caused by the differentγ-characteristics of the blocks is moderated.

Specifically, if A, B, C, D are the center positions of blocks B(I, J),B(I, J+1), B(I+1, J) and B(I+1, J+1) as shown in FIG. 27, aγ-characteristic for the illuminance nonuniformity correctioncorresponding to an arbitrary point P in an area AR1 enclosed by ABCD islinearly interpolated using the γ-characteristics for the illuminancenonuniformity correction set for the blocks B(I, J), B(I, J+1), B(I+1,J) and B(I+1, J+1). The γ-correction is applied to the pixel data in theposition P using this interpolated γ-characteristic.

Since the white saturation levels W_(A), W_(B), W_(C), W_(D) calculatedfor the respective blocks B(I, J), B(I, J+1). B(I+1, J) and B(I+1, J+1)are so dealt as to correspond to positions A, B, C, D, a value W_(P) ofthe white saturation level in position P is calculated by internallydividing the white saturation levels W_(A), W_(B), W_(C), W_(D) inpositions A, B, C, D in accordance with Equation (7). The interpolatedγ-characteristic for the illuminance nonuniformity correction inposition P is set using this value W_(P).W _(P)=(1−m)×{(1−n)×W_(A) +n×W _(C) }+m×{(1−n)×W_(B+n) ×W _(D})  (7)

According to the above interior division method, the γ-characteristicsare not interpolated in the portions of the respective blocks outsidetheir center positions in the blocks B(1, 1) to B(1, L), B(2, L) to B(k,L), B(K, L−1) to B(K, 1), B(k−1, 1) to B(2, 1) which are located aroundthe picked image. For these portions, the γ-characteristics may belinearly interpolated by an exterior division method.

The γ-characteristics may be interpolated in all positions except thecenter positions of the respective blocks B(I, J). However, a timerequired for the interpolation calculation may be shortened by dividingthe portion of each block B(I, J) except the center position intosub-blocks each including a plurality of pixel data (e.g., 4×4 to 6×6pixels) and linearly interpolating the γ-characteristic every sub-block.

The above interpolation of the γ-characteristics for the illuminancenonuniformity correction may be performed as follows. Since theγ-characteristics are set for the respective pixel positions, similarresults can be obtained if a block is set centering each pixel positionand the γ-characteristic is set using the histogram of level-frequencydistribution of the pixel data included in this block. However,according to this method, it disadvantageously takes a long time for thecalculation of the γ-characteristics because a huge number of blocks areset in the picked image G. Further, there is hardly any difference inthe generated histogram of level-frequency distributions betweenneighboring blocks because most of the pixel data are repeated inneighboring blocks. Thus, it is not practical to generate the histogramof level-frequency distribution for both blocks. Therefore, thisembodiment adopts the linear interpolation of the γ-characteristicswhich enables a high speed calculation and allows a reduced memorycapacity.

FIG. 14 is a block diagram showing the construction for applying animage processing to a color image from the oblique image correctiondevice 321 to the first and second γ-correction devices 326, 327.

The oblique image correction device 321, the image memory 323, the firstγ-characteristic setting device 324, the first and second γ-correctiondevice 326, 327 and the switch circuit 328 have each three processingcircuits of identical construction in correspondence with the pixel dataof the respective color components R, G, B.

For example, the pixel signals of red components are temporarily storedin the image memory 323A after having an image distortion corrected inthe oblique image correction device 321A. In the natural image mode, thepixel data of red components stored in the image memory 323A aretransferred via the switch circuit 328A to the first γ-correction device326A, where the 7-correction is performed using a predeterminedγ-characteristic for the natural images.

On the other hand, in the character image mode, the firstγ-characteristic setting device 324A sets a γ-characteristic for theilluminance nonuniformity correction block by block based on thehistogram of level-frequency distribution of the pixel data of Rincluded in each block, and the second γ-characteristic setting device325 sets a γ-characteristic for the black intensification based on anadjustment value of the black density adjustment switch 18. The pixeldata of red components stored in the image memory 323A are transferredvia the switch circuit 328 to the second γ-characteristic correctiondevice 327A, where the γ-correction is performed using theγ-characteristic for the black in tensification for each block after theγ-correction is performed using the γ-characteristic for the illuminancenonuniformity correction.

The pixel signals of green and blue components are processed in a mannersimilar to those of red components.

FIG. 15 is a block diagram showing the internal construction of thefirst γ-characteristic setting device 324.

In FIG. 15, a block size setting device 324 a is adapted to set the sizeof the blocks for dividing the picked image into small images in theblocks B(I, J). The block size setting device 324 a sets a block size Susing the image capturing magnification m inputted from the CPU 30, thepredetermined reference size S0 and the reference image capturingmagnification m0.

An address generator 324 b is adapted to generate addresses of the pixeldata included in each block B(I, J) based on the block size S0 set bythe block size setting device 324 a. This address data is used for theread control of the pixel data from the image memory 323 and theinterpolation calculation in a white saturation level interpolationcalculator 324 e.

A histogram generator 324 c is adapted to generate, for each block B(I,J), the histogram of level-frequency distribution (see FIG. 23) of thepixel data included in the block. A white saturation level settingdevice 324 d is adapted to set the white saturation level W (see FIG.24) of the γ-characteristic corresponding to the center position of eachblock B(I, J) using the histogram of level-frequency distributiongenerated by the histogram generator 324 c. The white saturation levelinterpolation calculator 324 e is adapted to interpolate the whitesaturation levels W of the γ-characteristics corresponding to thepositions of each block B(I, J) except the center position thereof usingthe white saturation level W set for each block B(I, J).

A γ-characteristic setting device 324 f is adapted to set theγ-characteristics for the illuminance nonuniformity correctioncorresponding to the respective pixel data of the picked image using thewhite saturation levels W set by the white saturation level settingdevice 324 d and the white saturation level interpolation calculator 324e.

Referring back to FIG. 13, a card driver 33 controls the driving of theHD card 13 to store the image data. An emission controller 34 controlsthe firing of the flash 7.

An LCD driver 35 controls the display of the picked image on the LCDdevice 19 in accordance with a control signal from the CPU 30. A memory36 stores a data (object distance Di and image capturing magnificationmi in each pixel position of the CCD 22) necessary for the oblique imagecorrection calculated by the CPU 30.

A lens driver 37 controls the focusing of the taking lens 2 inaccordance with an AF control value inputted from the CPU 30. A zoomdriver 38 controls the zooming of the taking lens 2 in accordance with adrive signal inputted from the CPU 30. A diaphragm driver 39 controlsthe aperture of the diaphragm 21 in accordance with the aperture valueAv of the exposure control values inputted from the CPU 30.

The light meter 40 include light receiving elements such as SPCsprovided behind the light meter window 3 and is adapted to measure thebrightness of an object. The distance meter 41 detects an objectdistance and include a light emitting portion 411 provided behind thelight emission window 4 for emitting infrared rays and a light receivingportion 412 provided behind the light receiving window 5 for receivingthe infrared rays reflected by the object.

The CPU 30 centrally controls the image capturing operation of thecamera 1. The CPU 30 includes an image capturing magnificationcalculator 301 for calculating an object distance D_(A) at a meteringpoint (center position A of the sensing surface of the CCD 22) detectedby the distance meter 41 and an image capturing magnification m_(A) atthis metering point, and image capturing magnifications mi, mi′ in otherpixel positions in the oblique image correction mode. The CPU 30 alsoincludes an exposure control value calculator 302 for calculatingexposure control values (aperture value Av and shutter speed Tv) basedon the brightness information of the object detected by the light meter40, and outputs the calculation result to the diaphragm driver 39 andthe CCD driver 31. The CPU 30 also includes an AF control valuecalculator 303 for calculating a lens drive amount by which the takinglens 2 is driven to attain an in-focus condition based on the objectdistance D_(A) detected by the distance meter 41 and outputs thecalculation result to the lens driver 37 as an AF control value.

Next, an image capturing control of the electronic camera 1 is describedwith reference to flowcharts of FIGS. 28 to 32. It is assumed that theimage capturing/reproduction switch 12 is set at the image capturingside.

When the electronic camera 1 is activated by turning the main switch 14on, the image capturing operation is enabled. When the zoom switch 11 isoperated in this state (YES in Step #2), the zoom lens of the takinglens 2 is driven according to the operating direction and the operatingamount of the zoom switch 11, thereby changing the zooming ratio (Step#4). Thereafter, when the shutter release button 10 is partly pressed toturn the ST1 switch on (YES in Step #6), this routine proceeds to Step#8 to start the image capturing preparation processing.

Specifically, it is first judged based on the set position of theoperation button 16 c of the mode setting switch 16 whether the obliqueimage capturing mode is set (Step #8). If the oblique image capturingmode is set (YES in Step #8), the angle of inclination θ is obtainedbased on the set position of the operation button 16 c (Step #10) and acorrection calculation is instructed to the oblique image correctiondevice 321 (Step #12). On the other hand, if the oblique image capturingmode is not set (NO in Step #8), Steps #10, #12 are skipped.

Subsequently, it is judged whether the illuminance nonuniformitycorrection has been designated (the illuminance nonuniformity correctionswitch 17 is set “on”) (Step #14). If the illuminance nonuniformitycorrection has been designated (YES in Step #14), the densityinformation on the character portion is obtained based on the setposition of the black density adjustment switch 18 (Step #16). Then, thefirst γ-characteristic setting device 324 is set ready for theprocessing; the density information is inputted to the secondγ-characteristic setting device 325; the γ-characteristic for the blackintensification is set based on the density information; and theγ-characteristic for the black intensification is inputted to the secondγ-correction device 327 (Step #18). The first γ-correction device 326 isthen switched to the second γ-correction device 327 (Step #20). On theother hand, if the illuminance nonuniformity correction has not beendesignated (NO in Step #14), Steps #16 to #20 are skipped.

Subsequently, infrared rays for the distance metering are projectedtoward an object from the light emitting portion 411 of the distancemeter 41 (Step #22). A distance meter data is obtained by receiving theinfrared rays reflected by the object by the light receiving portion 412of the distance meter 41 (Steps #24, #26).

It is then judged whether the oblique image correction mode is set (Step#28 in FIG. 29). If the oblique image correction mode is set (YES inStep #28), a distance D_(A) from the sensing surface in the center ofthe field to the object (distance OP in FIG. 8) is calculated based onthe obtained distance meter data and angles of view αi, βi in each pixelposition of the CCD 22 are calculated.

An object distance Di in each pixel position (i.e., a distribution ofobject distance within the field) is calculated based on the angles ofview αi, βi, the object distance D_(A) and the angle of inclination θ,and the image capturing magnification m_(A) at the distance meteringpoint is calculated based on the focal length f and the object danceD_(A). The image capturing magnifications mi, mi′ in each pixel position(i.e., a distribution of image capturing magnifications within thefield) are calculated based on the image capturing magnification m_(A),the angle of inclination θ and the angles of view αi, βi in accordancewith Equations (1), (2). Further, magnifications ki, ki′ are calculatedin accordance with Equations (4) and (6) (Step #30).

Subsequently, an area of effective pixel data in the image after theoblique image correction (an area except the pixel positions of thedummy data, hereinafter, “data effective area”) is calculated withreference to a subroutine “Data Effective Area Calculation” shown inFIG. 31 (Step #32).

The data effective area is calculated as follows. First, a counter K forcounting the pixel position is set at “1” (Step #90). A pixel position(i′, j′) of the image in a pixel position at K=1 after the correction iscalculated based on the object distance Di, the angle of inclinations,and the focal length f of the taking lens 2 at K=1 (Step #92). As shownin FIG. 33, if g(i, j) denotes a pixel data in a pixel position (i, j),since the data effective area calculation is conducted along rasterdirection from the pixel position (1, 1), K=L·(I−1)+J. Thus, the pixeldata g(I, J) corresponds to the pixel data g(L (I-l)+J).

It is then judged whether the calculated pixel position (i′, j′) afterthe correction is located in an effective image area (Step #94). Thisjudgment is made by judging whether the pixel position (i′, j′) fallswithin a range of (1 to n, 1 to m) since the effective image area is (1to n, 1 to m). If the pixel position (i′, j′) after the correction fallswithin the effective image area (YES in Step #94), the data in thispixel position (i′, j′) is stored in the memory 36 (Step #96). Step #96is skipped unless the pixel position (i′, j′) after the correction is inthe effective image area.

After the count value of the counter K is incremented by “1” (Step #98),it is judged whether the count value K is larger than a total pixelnumber n·m (Step #100). If K≦n·m (NO in Step #100), this subroutinereturns to Step #90 to judge whether the pixel position of a next pixeldata g(K) after the correction is in the effective image area. If K>n·m(YES in Step #100), this subroutine returns on the judgment that thejudgment has been made for all pixel data.

Referring back to the flowchart of FIG. 29, if the usual image capturingmode is set in Step #28 (NO in Step #28), it is judged whether theilluminance nonuniformity correction has been designated (Step #34). Ifthe illuminance nonuniformity correction has not been designated (NO inStep #34), Steps #30, #32 are skipped. If the illuminance nonuniformitycorrection has been designated (YES in Step #34), Steps #30, #32 areskipped and a control signal representing the prohibition of the flashfiring is outputted to the emission controller 34 to prohibit the firingof the flash 7 (Step #36). The firing of the flash 7 is prohibited whenthe usual image capturing mode is set and the illuminance nonuniformitycorrection has been designated for the following reason. For example,there is a possibility that the flash 7 is automatically fired in ascene where the white board 20 is captured from front. In this scene,the flash light may be fully reflected by the white board 20, making thecharacters in the picked image unreadable. In order to prevent such anerror image capturing, the firing of the flash 7 is prohibited.

Subsequently, the lens drive amount for driving the taking lens 2 toattain an in-focus condition is calculated based on the object distanceD_(A) (Step #38), and the exposure control values are calculated basedon the light meter data detected by the light meter 40 (Step #40). Inthis way, the image capturing preparation is completed and theelectronic camera 1 waits on standby for the exposure.

In this standby state, when the shutter release button 10 is fullypressed to turn the ST2 switch on (YES in Step #42), this routineproceeds to Step #46 to perform the exposure. On the other hand, if theshutter release button 10 is kept partly pressed, i.e., the ST1 switchis on, the camera 1 continues to wait on standby for the exposure (aloop of Steps #42, #44). When the ST1 switch is turned off by releasingthe shutter release button 10 (NO in Step #44), this routine returns toStep #2.

Upon starting the exposure, a data on the lens drive amount is outputtedto the lens driver 38 and the taking lens 2 is focused (Step #46).Thereafter, the aperture value data Av of the exposure control values isoutputted to the diaphragm driver 39 and the aperture of the diaphragm21 is adjusted (Step #48).

Subsequently, it is judged whether the illuminance nonuniformitycorrection has been designated (Step #50). If the illuminancenonuniformity correction has been designated (YES in Step #50), the sizeof the blocks for dividing the picked image into a plurality of smallimages is set (Step #52). The block size is set as follows. The blocksize S (=S0·m_(A)/m0) in the center of the field is set using the imagecapturing magnification m_(A) calculated for the center of the field,the predetermined reference image capturing magnification m0 and theblock size S0, and this block size is applied as the block size in otherpositions. In other words, the picked image is divided by blocks of thesize set in the center of the field without changing the block sizedepending on the position in the field.

Further, the blocks missing the pixel data (blocks including the dummydata after the correction) within an area where the reduction processingis performed in the oblique image correction mode are extracted based onthe distribution of image capturing magnifications mi and the set blocksize (Step #54). Specifically, in the case that an oblique image G ofFIG. 34A is corrected into a front image G′ of FIG. 34B and this frontimage G′ is divided into 45 (=5×9) blocks, eleven blocks B(1, 1) to B(1,4), B(5, 1) to B(5, 4), B(5, 1) to B(5, 4) within a left half area ofthe image G′ having been subjected to the reduction processing areextracted as blocks missing the pixel data. On the other hand, unlessthe illuminance nonuniformity correction has been designated (NO in Step#50), the image processing is not performed block by block. Accordingly,Steps #52, #54 are skipped.

Subsequently, the shutter speed data calculated in Step #40 is outputtedto the CCD driver 31 to start the image pickup operation (integration)by the CCD 22 (Step #56). The CCD 22 picks up an object image by storingelectric charges (electric charge integration) in a photosensitiveportion for a predetermined time after discharging the electric chargesin the photosensitive portion in accordance with a drive control signalfrom the CCD driver 31.

Upon the completion of the image pickup operation by the CCD 22, thereading of the electric charges (pixel data) stored in the respectivepixels of the photosensitive portion to the image processor 32 isstarted (Step #58). The pixel data in the CCD 22 are successively readalong a direction of arrow every vertical line as shown in FIG. 33 andinputted to the image processor 32.

Subsequently, it is judged whether the oblique image correction mode isset (Step #60 in FIG. 30). If the oblique image correction mode is set(YES in Step #60), the oblique image correction device 321 applies theoblique image correction to the pixel data read from the CCD 22 (Step#62). The oblique image correction is-performed every vertical line. Inthe region where the reduction processing is to be performed, there isan area where the pixel data are going to be lost. The oblique imagecorrection is performed by filling this area with predetermined dummydata (e.g., white data). As shown in FIGS. 35A and 35B, pixel data g1,g1′, g2, g2′ at the opposite ends of the lines may be, for example,interpolated as dummy data g3, g3′ in the pixel positions (hatchedpositions in FIG. 35A) where pixel data are missing along verticaldirection, the entire pixel data g4 of a known line may be, for example,interpolated as dummy data g5 in the pixel positions (hatched positionsin FIG. 35B) where pixel data are missing along row direction. The pixeldata after the oblique image correction are stored in the image memory323.

If the blocks missing the pixel data have been extracted in Step #54,the data effective area is calculated every block (Step #64).

It is then judged whether the illuminance nonuniformity correction hasbeen designated (Step #66). Unless the illuminance nonuniformitycorrection has been designated (YES in Step #66), the firstγ-characteristic setting device 324 sets the γ-characteristic for theilluminance nonuniformity correction every block in accordance with asubroutine “γ-characteristic Setting” shown in FIG. 32 (Step #68).

The γ-characteristic for the illuminance nonuniformity correction is setfor each block as follows. First, a count value of a counter M forcounting the block number is set at “1” (Step #110). Since the order ofthe blocks in the γ-characteristic setting is along raster direction inthe block division shown in FIG. 20, M=L·(I−1)+J. Thus, the block B(I,J) corresponds to the block B(L·(I−1)+J).

Subsequently, all pixel data in the data effective areas included in theblock B(M) are read (Step #112), and a histogram of level-frequencydistribution as shown in FIG. 23 is generated using the pixel dataexcept X % of pixel data at the high level side (Step #114). Then, thelevel w corresponding to the peak value of the convex portion Ucorresponding to the white portion of the histogram of level-frequencydistribution is calculated (Step #116) and is stored as a whitesaturation level W(M) of the γ-characteristic for the block B(M) (Step#118).

After the count value of the counter M is incremented by “1” (Step#120), it is judged whether the count value M is larger than the totalblock number n K·L) (Step #122). If M≧n (NO in Step #122), thissubroutine returns to Step #110 to set a white saturation level W(I) fora next block B(M) (Steps #112 to #120). If M>n (YES in Step #122), thissubroutine returns upon the judgment that the setting of the whitesaturation level W(M) of the γ-characteristic has been completed for allblocks B(M).

Referring back to the flowchart of FIG. 30, the white saturation levelW(I) of the γ-characteristic for the illuminance nonuniformitycorrection set for each block B(I) is interpolated to set theγ-characteristics for the illuminance nonuniformity correction in thepixel positions except the center position of each block B(I) (Step#70). While the set γ-characteristics are inputted to the secondγ-correction device 327, the pixel data are transferred from the imagememory 323 to the second γ-correction device 327. After being subjectedto the γ-correction using the γ-characteristic for the illuminancenonuniformity correction corresponding to the pixel position, the pixeldata is subjected to the γ-correction using the γ-characteristic for theblack intensification (Step #72).

On the other hand, if the illuminance nonuniformity correction has beendesignated in Step #66 (NO in Step #66), the pixel data are transferredfrom the image memory 323 to the first γ-correction device 326 and aresubjected to the γ-correction using a predetermined γ-characteristic forthe natural images (Step #74).

The pixel data having been subjected to the image processing such as theγ-correction are successively written in the HD card 13 (a loop of Steps#66 to #76). Upon the completion of the writing of all pixel data in theHD card 13 (YES in Step #76), a control signal representative of thecompletion of the reading of the pixel data is outputted to the CCDdriver 31 and a control signal representative of the completion of thewriting of the pixel data is outputted to the card driver 33 (Step #78).In this way, the image pickup operation of one frame of image iscompleted and this routine returns to Step #2 to perform the next imagepickup operation.

In the first embodiment, the histogram of level-frequency distributionis generated using only the effective pixel data in the blocks includingthe dummy data in the illuminance nonuniformity correction for the imageafter the oblique image correction, and the γ-characteristics for theilluminance nonuniformity correction for these blocks are set using thewhite saturation levels W determined by the histogram of level-frequencydistributions. However, for such blocks, instead of setting theγ-characteristics for the illuminance nonuniformity correction based onthe level distribution of the pixel data included in the blocks, theinclination γ-characteristic for the illuminance nonuniformitycorrection set for the neighboring blocks including no dummy data may beapplied.

Specifically, since the dummy data is included in, for example, theblocks B(1, 1), B(1, 2), B(2, 1) in FIG. 34B, the γ-characteristic forthe illuminance nonuniformity correction set for the more adjacent blockB(2, 2) is applied for these blocks B(1, 1), B(1, 2), B(2, 1). Likewise,the γ-characteristic for the illuminance nonuniformity correction setfor the most adjacent block B(2, 3) including no dummy data is appliedfor the block B(1, 3) and the γ-characteristic for the illuminancenonuniformity correction set for the most adjacent block B(3, 23)including no dummy data is applied for the block B(3, 1).

In this case, the pixel data are processed as follows in FIG. 15.Specifically, the address generator 324 b divides the picked image intoa plurality of blocks B(I, J) based on the block size inputted from theblock size setting device 324 a, extracts the blocks B(I, J) includingthe dummy data based on the information on the data effective areasinputted from the data effective area calculator 322, and calculates themost adjacent blocks B(I, J) including no dummy data for the respectiveextracted blocks B(I, J). The calculation result is inputted from theaddress generator 324 b to the white saturation level setting device 324d as indicated by dotted line in FIG. 15.

The pixel data are read from the image memory 323 block by block foronly the blocks B(I, J) including no dummy data, and the histogram oflevel-frequency distribution of all pixel data included in each suchblock is generated in the histogram generator 324 c to set the whitesaturation level W. The white saturation level setting device 324 dallocates the white saturation level W set for the corresponding mostadjacent block B(I, J) to each block B(I, J) including the dummy databased on the information of the most adjacent block B(I, J) including nodummy data for the block B(I, J) including the dummy data inputted fromthe address generator 324 b.

In the case that the area of the white portion in the data effectiveareas in the block is small, the convex portion U corresponding to thewhite portion may not be clearly shown in the histogram oflevel-frequency distribution of the pixel data within the data effectiveareas. Thus, the reliability of the white saturation level W of theγ-characteristic for the illuminance nonuniformity correction set basedon this histogram of level-frequency distribution is questionable. Themethod for applying the γ-characteristic set for the most adjacent blockincluding no dummy data has an advantage of solving the problem of thereliability of the characteristic. Further, since the γ-characteristicof the most adjacent block is applied, there is no likelihood that apseudo boundary line is created due to the discontinuous image qualitycaused by a sudden change of the γ-characteristic between the blocks.

FIG. 36 is a block construction diagram of an electronic camera 1according to a second embodiment, FIG. 37 is a detailed block diagram ofthe construction for applying an image processing to a color image fromthe A/D convert 320 to the first and second γ-correction devices 326,327, and FIG. 38 is a block diagram showing the internal construction ofthe first γ-characteristic setting device 324 according to the secondembodiment.

The electronic camera 1 according to the second embodiment isconstructed such that the oblique image correction is performed afterthe illuminance nonuniformity correction is performed. In other words,the processing order of the illuminance nonuniformity correction and theoblique image correction is opposite from that of the electronic camera1 according to the first embodiment.

The methods according to the second embodiment for performing theilluminance nonuniformity correction and the oblique image correctionare basically identical to those described in the first embodiment.Accordingly, description is supplementarily given on processings whichare differed by reversing the processing order of the illuminancenonuniformity correction and the oblique image correction.

The block construction diagram of FIG. 36 differs from that of FIG. 13only in the internal construction of an image processor 32.Specifically, the image processor 32 shown in FIG. 36 differs from thatshown in FIG. 13 in that the data effective area calculator 322 isdeleted, the oblique image correction device 321 provided between theA/D converter 320 and the image memory 323 is provided after the secondγ-correction device 327, and a switch circuit 329 is added after thefirst and second γ-correction devices 326, 327.

In FIG. 36, the switch circuit 328 switches the connection of the imagememory 323 with the first and second γ-correction devices 326, 327, andthe switch circuit 329 switches the connection of the first γ-correctiondevice 326 and the oblique image correction device 321 with the HD card13. The switching of the switch circuits 328, 329 is controlled inaccordance with a control signal outputted from the CPU 30 in conformitywith the set state of the illuminance nonuniformity correction switch17. If the illuminance nonuniformity correction switch 17 is set “OFF”(if the natural image mode is set), the image memory 323 and the firstγ-correction device 326 are connected and the first γ-correction device326 and the HD card 13 are connected. If the illuminance nonuniformitycorrection switch 17 is set “ON” (if the character image mode is set),the image memory 323 and the second γ-correction device 327 areconnected and the oblique image correction device 321 and the HD card 13are connected.

In the above construction, the illuminance nonuniformity correctingmethod in the usual image capturing mode is same as the one describedabove with reference to FIGS. 19 to 21. However, in the oblique imagecorrection mode, the block size in the illuminance nonuniformitycorrection is changed within a field as shown in FIG. 39B since theoblique image correction is performed after the illuminancenonuniformity correction is performed. In the oblique image capturing,the image capturing magnification mi differs within the field. As shownin FIG. 39A, the character size is small in positions where the imagecapturing magnification mi is small while being large in positions wherethe image capturing magnification mi is large. Accordingly, if the fieldis divided by blocks of the same size, the number of characters includedin the blocks changes and, therefore, all blocks cannot be set in propersize. Thus, the size of the respective blocks is determined accordingthe image capturing magnification mi in the oblique image correctionmode.

Specifically, the proper size S of the block is calculated from theimage capturing magnification m in the center of the field according tothe aforementioned method, and the size Si of the block in a positionother than the center of the field is calculated based on the propersize S, the image capturing magnification mi (or mi′) in this positioncalculated from the angle of inclination θ, the angle of view α (or γ)and the image capturing magnification m in the center of the field inaccordance with Equations (1) and (2): Si=S·mi/m. Since the imagecapturing magnification varies only along row direction in an example ofFIG. 39B, the block size is changed along horizontal direction. Further,in FIG. 39B, the field is divided into three areas: a central area, aleft area and a right area, and a block size in conformity with theimage capturing magnification is set for each area. This division isonly an example, and the field may be divided into four or more areas inthe case where the angle of inclination θ is considerably large.Although a case where the sensing surface is not inclined with respectto the object surface along vertical direction is described in thisembodiment, the block size is changed also according to the imagecapturing magnification along vertical direction in the case that thesensing surface is inclined along vertical direction.

The block construction diagram of FIG. 37 differs from that of FIG. 14in that the data effective area calculator 323 is deleted and theoblique image correction device 321 is replaced by the A/D converter320.

In FIG. 37, the image memory 323, the first γ-characteristic settingdevice 324, the first and second γ-correction devices 326, 327 and theswitch circuit 328 are each provided with three processing circuits ofidentical construction so as to correspond to the pixel data of therespective color components R, G, B.

For example, the pixel signal of R is temporarily stored in the imagememory 323A after being A/D converted into an image data in the A/Dconverter 320A. In the natural image mode, the pixel data of R stored inthe image memory 323A is transferred to the first γ-correction device326A via the switch circuit 328, and γ-correction is applied theretousing a specified γ-characteristic for the natural images.

On the other hand, in the character image mode, a γ-characteristic forthe illuminance nonuniformity correction is set every block by the firstγ-characteristic setting device 324A based on the histogram oflevel-frequency distribution of the pixel data of R included in eachblock, and a γ-characteristic is set by the second γ-characteristicsetting device 325 based on the adjustment value of the black densityadjustment switch 18. The pixel data of R stored in the image memory323A is transferred to the second γ-correction device 327A via theswitch circuit 328, and γ-correction is applied thereto every blockusing the γ-characteristic for the black density adjustment afterγ-correction is applied using the γ-characteristic for the illuminancenonuniformity correction.

The pixel signals of G and B are processed in the similar manner as thepixel signal of R.

The block construction diagram of FIG. 38 differs from that of FIG. 15in that the data effective area calculator 323 is deleted and the imagememory 323 is replaced by the CCD 22 and the A/D converter 320.

In FIG. 38, the histogram generator 324 c to the γ-characteristicsetting device 324 f perform the same operation as those shown in FIG.15. The block size setting device 324 a is adapted to set the sizes ofthe blocks B(I, J) for dividing the picked image into small images. Inthe usual image capturing mode, the block size setting device 324 a setsthe block size S based on the image capturing magnification m in thecenter of the field, the preset reference size S0 and the referenceimage capturing magnification m0 which are inputted from the CPU 30 inorder to divide the picked image into blocks of the same size. In theoblique image correction mode, the block size setting device 324 a setsthe block size S in the center of the field and the block sizes Si inpositions other than the center of the field based on the imagecapturing magnifications mi (or mi′) other than the center of the field,the image capturing magnification m in the center of the field and theblock size S in order to divide the picked image into blocks ofdifferent sizes.

The address generator 324 b generates the addresses of the pixel dataincluded in each block B(I, J) in accordance with the block size S (orSi) set by the block size setting device 324 a. This address data areused for the reading of the pixel signals from the CCD 22 and for theA/D conversion in the A/D converter 320 as well as for the interpolationcalculation in the white saturation level interpolation calculator 324e.

Next, an image capturing control of the electronic camera 1 according tothe second embodiment is described with reference to flowcharts of FIGS.40 to 43.

FIGS. 40 to 42 are a main routine of the image capturing control. Theimage capturing procedure of the electronic camera 1 of the secondembodiment is mostly common to that of the electronic camera 1 of thefirst embodiment. Specifically, the flowchart shown in FIGS. 40 to 42differ from that of FIGS. 28 to 30 in that Steps #32, #54 are deletedand a processing of Steps #73-1 to 73-3 is inserted between Steps #72and #74 instead of Steps #60 to #64.

The processing of Step #32 is deleted because it concerns the dataeffective area calculator 322 which is not provided in the secondembodiment. The processing of Step #54 is deleted because it concernsthe oblique image correction and is, accordingly, not necessary beforethe illuminance nonuniformity correction in the second embodiment inwhich the oblique image correction is performed after the illuminancenonuniformity correction. The addition of Steps #73-1 to #73-3 insteadof Steps #60 to #64 is made to perform the oblique image correctionafter the illuminance nonuniformity correction.

FIG. 43 is a flowchart showing a subroutine “Block Size Setting”executed in Step #52. Since the block size changes according to theimage capturing magnification within the field in the second embodiment,this processing is added.

The flowcharts shown in FIGS. 40 to 42 are a modification to theflowcharts shown in FIGS. 28 and 30 as described above, and asubstantially amended part is Step #52 and Step #58 and subsequentsteps. Accordingly, description is centered on the content concerningthe amended part here.

After the electronic camera 1 is activated (a loop of Steps #2 to #6),the shutter release button 10 is partly pressed to turn the ST1 switchon (YES in Step #6). Then, a processing for the image capturingpreparation is performed in Steps #8 to #40.

In this image capturing preparation processing, after the setting of theoblique image correction mode and preparation according to whether ornot the illuminance nonuniformity correction is to be performed (readingof the angle of inclination θ, calculation of the distribution of imagecapturing magnifications, reading of the density information, switch ofthe γ-correction device of the image processor 32), the exposure controlvalues and AF control value are calculated. In the processing of Step#20 for switching the γ-correction device, the switch circuits 328, 329switch the signal processing from the one performed by the firstγ-correction device 326 to the one performed by the second γ-correctiondevice 327 and the oblique image correction device 321. Since theoblique image correction is not performed before the illuminancenonuniformity correction, the data effective area calculation for theilluminance nonuniformity correction is not performed.

When the shutter release button 10 is fully pressed to turn the ST2switch on after the image capturing preparation processing is completedand the camera 1 waits on standby for an exposure operation (a loop ofSteps #2 to #44), this routine proceeds to Step #46 to perform theexposure operation.

Upon starting the exposure operation, a data on the lens drive amount isoutputted to the lens driver 37 and the taking lens 2 is driven toattain an in-focus condition (Step #46). Thereafter, the aperture valuedata Av of the exposure control values is outputted to the diaphragmdriver 39 to adjust the aperture of the diaphragm 21.

Subsequently, it is judged whether the illuminance nonuniformitycorrection has been designated (Step #50 in FIG. 42). If the illuminancenonuniformity correction has been designated (YES in Step #50), thesizes of a plurality of blocks for dividing the image are set inaccordance with the subroutine “Block Size Setting” shown in FIG. 43(Step #52).

The block size is set as follows. First, the image capturingmagnification m_(A) in the center position of the field is calculatedbased on the focal length f and the object distance D_(A) measured forthe center of the field (Step #130). Subsequently, the block size S(=S0·m_(A)/m0) for the center position of the field is calculated basedon the image capturing magnification mA, the reference image capturingmagnification m0 and the block size S0 (Step #132).

Subsequently, it is judged whether the oblique image correction mode isset (Step #134). Unless the oblique image correction mode is set (NO inStep #134), the block size of the center of the field calculated in Step#132 is set as a block size for regularly dividing the picked image bythe blocks (Step #140) and this subroutine returns.

On the other hand, if the oblique image correction mode is set (YES inStep #134), the image capturing magnifications mi, mi′ in the respectivepixel positions (i.e., distribution of image capturing magnificationswithin the field) are calculated based on the image capturingmagnification m_(A) calculated in Step #130, the angle of inclination θset by the mode setting switch 16 and the angles of view αi, βi in therespective pixel positions calculated in Step #30 in accordance withEquations (1) and (2) (Step #136). Subsequently, the block sizes Si forthe illuminance nonuniformity correction in the respective pixelpositions are calculated based on the distribution of image capturingmagnifications and the block size S in the center of the field (Step#138). The block sizes for dividing the field by the blocks of sizeswhich differ according to the image capturing magnification are setbased on the above calculation result (Step #140) and this subroutinereturns.

Upon the completion of the setting of the block sizes, the data on theshutter speed calculated in Step #40 is outputted to the CCD driver 31to start the image pickup operation (integration) by the CCD 22 (Step#56). After resetting the electric charges in the photosensitive portionin accordance with a drive control signal from the CCD driver 31, theCCD 22 picks up an object image by storing electric charges (electriccharge integration) in the photosensitive portion for a predeterminedtime.

Upon the completion of the image pickup operation by the CCD 22, thereading of the electric charges stored in the respective pixels of thephotosensitive portion (pixel data) to the image processor 32 is started(Step #58). The pixel data of the CCD 22 are successively read in arrowdirection every vertical line and inputted to the image processor 32.After being converted into pixel data in the A/D converter 320, thepixel signals inputted to the image processor 32 are stored in the imagememory 323 and inputted to the first γ-characteristic setting device324.

It is then judged whether the illuminance nonuniformity correction hasbeen designated (Step #66). If the illuminance nonuniformity correctionhas been designated (YES in Step #66), the first γ-characteristicsetting device 324 sets a γ-characteristic for the illuminancenonuniformity correction block after block in accordance with thesubroutine “γ-Characteristic Setting” shown in FIG. 32 (Step #68). Sincethis γ-characteristic setting is same as the aforementioned one, nodescription is given here.

Subsequently, the white saturation level W(I) of the γ-characteristicfor the illuminance nonuniformity correction set for each block B(I) isinterpolated, and γ-characteristics for the illuminance nonuniformitycorrection in the pixel positions of each block B(I) other than thecenter position thereof are set (Step #70). While the setγ-characteristics are inputted to the second γ-correction device 327,the pixel data are transferred from the image memory 323 to the secondγ-correction device 327 via the switch circuit 328. After γ-correctionis applied to the pixel data using the γ-characteristics for theilluminance nonuniformity correction corresponding to the respectivepixel positions, γ-correction is further applied using theγ-characteristics for the black intensification.

It is then judged whether the oblique image correction mode is set (Step#73-1). If the oblique image mode is set (YES in Step #73-1), theoblique image correction is applied to the pixel data outputted from thesecond γ-correction device 327 by the oblique image correction device321 (Step #73-2). The oblique image correction is performed everyvertical line. In an area where the reduction processing is to beperformed, the oblique image correction is performed by filling a pixeldata missing area with the preset dummy data (e.g., white data).

On the other hand, if the natural image mode is set in Step #66 (NO inStep #66), the pixel data are transferred from the image memory 323 tothe first γ-correction device 326 via the switch circuit 328, andγ-correction is applied thereto using the preset γ-characteristic forthe natural images (Step #73-3). The pixel data after the γ-correctionis written in the HD card 13 via the switch circuit 329 (Step #74).

The pixel data having been subjected to the oblique image correction inthe character image mode or those having been subjected to theγ-correction in the natural image mode are successively written in theHD card 13 via the switch circuit 328 (a loop of Steps #66 to #76). Uponthe completion of the writing of all pixel data in the HD card 13 (YESin Step #76), a control signal indicative of the completion of thereading of the pixel data is outputted to the CCD driver 31 and acontrol signal indicative of the completion of the writing of the pixeldata is outputted to the card driver 33 (Step #78). In this way, theimage pickup operation of one frame of image is completed and thisroutine returns to Step #2 to perform a next image pickup operation.

Since the oblique image correction is performed after the illuminancenonuniformity correction in the second embodiment, processings such asthe one to generate a histogram of level-frequency distribution bydeleting the dummy data are not necessary unlike the first embodiment.Accordingly, the second embodiment has an advantage of securelyperforming the suitable illuminance nonuniformity correction withoutcomplicating the processings.

In the first and second embodiments, histogram of level-frequencydistributions are generated for all set blocks B(I, J) and the whitesaturation levels W of the γ-characteristics for the illuminancenonuniformity correction are set based on these histogram oflevel-frequency distributions. However, in the case that illuminance isrelatively uniform along vertical direction, but considerably varyingonly along horizontal direction, the histogram of level-frequencydistributions may be generated only for a row of blocks B(3, 1), B(3,2), . . . B(3, 9) located in the middle of the picked image G as shownin FIG. 44 and the white saturation levels W of the γ-characteristicsmay be set based on these histogram of level-frequency distributions.For the other blocks B(I, J) (I=1, 2, 4, 5, J=1, 2, . . . 9), theγ-characteristics set for the block B(3, r) in the columns includingthese blocks may be used. For example, the γ-characteristic set for theblock B(3, 1) is used for the blocks B(1, 1), B(2, 1), B(4, 1), B(5, 1)in the first column.

Conversely, in the case that illuminance is relatively uniform alonghorizontal direction, but considerably varying only along verticaldirection, the histogram of level-frequency distributions may begenerated only for a column of blocks B(1, 5), B(2, 5), . . . B(5, 5)located in the middle of the picked image G as shown in FIG. 45 and thewhite saturation levels W of the γ-characteristics may be set based onthese histogram of level-frequency distributions. For the other blocksB(I, J) (I=1, 2, . . . 5, J=1 to 4, 6 to 9), the γ-characteristics setfor the block B(r, 5) in the rows including these blocks may be used.For example, the γ-characteristic set for the block B(1, 5) is used forthe blocks B(1, 1), B(1, 2), B(1, 3). B(1, 4), B(1, 6), B(1, 7), B(1,8), B(1, 9) in the first row. By doing so, the calculation time forγ-characteristics can be shortened and the capacity of the memory forstoring the set γ-characteristics can be reduced.

Although the entire picked image G is divided in columns and rows into amatrix form, thereby continuously setting the blocks B(I, J) in theforegoing embodiments, a plurality of blocks B(I, J) may be discretelyset in the picked image G. By doing so, the number of the blocks can bereduced. Therefore, similar to the above example, the calculation timefor γ-characteristics can be shortened and the capacity of the memoryfor storing the set γ-characteristics can be reduced.

In the first and second embodiments, the case where the image distortioncorrecting function of correcting a perspective geometric distortion inoblique image capturing and the illuminance nonuniformity correctingfunction are combined is described. However, the present invention isnot limited to the above case, but may be applicable to a case where animage distortion correcting function of correction a geometricdistortion caused by the optical characteristic of the optical imagepickup system and a geometric distortion caused by the characteristic ofthe signal processing system and the illuminance nonuniformitycorrecting function are combined.

As described above, according to the method for dividing the pickedimage into blocks and detecting the level of the base portion (whiteportion) of each block based on the histogram of level-frequencydistribution of the pixel data included in each block, if the whiteportion (e.g., a background portion such as a white wall standing behindthe white board 20) except the white board portion is included in theblock, the histogram of level-frequency distribution is not a typicaltwo-peak distribution as shown in FIG. 19. Accordingly, it is difficultto accurately detect the white level of the white board 20.

Thus, if the illuminance nonuniformity correction is performed in thecase of, e.g., monochromatic image capturing, the white board portionturns blackish particularly in the blocks including the white boardportion and the background portion. Such a false coloring phenomenonoccurs because the white saturation level set by the histogram oflevel-frequency distribution is improper.

Specifically, in the blocks including the white board portion and thebackground portion as shown in FIG. 47, the histogram of level-frequencydistribution of the pixel data has two convex portions U1, U2 in gray towhite areas in correspondence with the white board portion and thebackground portion as shown in FIG. 48. Since the histogram oflevel-frequency distribution of FIG. 48 is for the block at theperiphery of the white board 20 where no characters are drawn, theconvex portion C corresponding to the character portion shown in FIG. 19is not seen there.

For example, if the brightness of the background portion is higher thanthat of the white board portion as in the case where the white board 20is placed before a white wall having high index of reflection, theconvex portion U1 corresponds to the background portion and the convexportion U2 corresponds to the white board portion. Accordingly, if theγ-correction is performed using the γ-characteristic set using the levelw corresponding to the peak value of the convex portion U1 as the whitesaturation level W, a part of the background portion above the whitesaturation level W is uniformly converted into a specific white portion,whereas a part of the white board portion below the white saturationlevel W is a gray area and is converted into a specific gray portion.

Thus, if the γ-correction is performed using the γ-characteristic forthe black intensification thereafter, a portion of the white boardportion below the black saturation level B is converted into black andturns to be a black portion in the white board portion.

FIGS. 49A to 49C are graphs for explaining why black coloring occurs dueto the aforementioned γ-correction for the black intensification andγ-correction for the illuminance nonuniformity correction, wherein FIG.49A shows a histogram of level-frequency distribution. FIG. 49B shows aγ-characteristic for the illuminance nonuniformity correction set basedon the histogram of level-frequency distribution, and FIG. 49C shows aγ-characteristic for the black intensification.

The white saturation level W of the γ-characteristic shown in FIG. 49Bis set at a level w (=200) corresponding to the peak value of a convexportion U1 corresponding to the background portion of the histogram oflevel-frequency distribution shown in FIG. 49A. Accordingly, if a levelw′ corresponding to the peak value of a convex portion U2 correspondingto the white board portion is assumed as a white level representing thewhite board portion, the white board portion having the level value“100” is converted into a level value “127” by the γ-characteristicshown in FIG. 49 after the 7-correction. Thereafter, when theγ-correction is performed using the γ-characteristic for the blackintensification in which the black saturation level B is set at “170”, apart of the white board portion below the black saturation level B isconverted into a level value “0”, i.e., converted into a black color.

On the other hand, in the case that the level of the white board portionis lower than that of the background portion as shown in FIG. 50A andthe area of the white board portion in the block is larger than that ofthe background portion, and a level w′ (=100) corresponding to the peakvalue of a convex portion U2 corresponding to the white board portion isset as the white saturation level W as shown in FIG. 50B, even if theblack intensification is performed using the same γ-characteristic asthe one of FIG. 49C, the level value of the white board portionconverted into “255” by the γ-characteristic for the illuminancenonuniformity correction is kept “255” without being converted to “0”.Thus, the white board portion can be properly made white.

In color image capturing, the γ-characteristic is set for theilluminance nonuniformity correction for each of the color components R,G, B. If the white saturation level is determined by the level of thebackground portion in the setting of the γ-characteristic of any of thecolor components, false coloring occurs in the white board portion afterthe γ-corrections for the illuminance nonuniformity correction and theblack intensification.

Let it be assumed that W_(R), W_(G), W_(B) denote the white saturationlevels of the γ-characteristics of the color components R, G, B,respectively. If the white saturation level W_(R) is set as in theexample of FIG. 50 and the white saturation levels W_(G), W_(B) are setas in the example of FIG. 49, the red components of the white boardportion DR is converted to 255 as described in the example of FIG. 50and the green and blue components D_(G), D_(B) thereof are converted to0 as described in the example of FIG. 49 when the γ-correction isapplied to the white board portion where, for example, the colorcomponents D_(R), D_(G), D_(B) are: D_(R)=200, D_(G)=D_(B)=00.Accordingly, the white board portion is colored in red.

In the case of color-image capturing the white board 20 as well as thebackground, the image quality is considerably reduced if coloringphenomenon occurs during the image processing in the white board portionin a boundary area between the white board portion and the backgroundportion of the picked image, making the image difficult to see. Thus, itis desirable to prevent the above coloring phenomenon as much aspossible.

In order to securely prevent the above coloring phenomenon, an imagecapture person may frame such that the entire image of the white board20 falls within the field. However, since a desired angle of view maynot be necessarily constantly obtained, it is better to reduce thecoloring phenomenon during the image processing.

As a method for reducing the coloring phenomenon during the imageprocessing, there can be considered a method for generating a histogramof level-frequency distribution excluding the pixel data of a portion(background portion) of the block except the white board portion.According to this method, only the white board portion in the pickedimage needs to be recognized. For example, the picked image may bedisplayed on the LCD device 19 in the exposure standby state, and anarea designation member may be provided to designate an area on themonitor display, so that an image capture person can designate and inputonly the white board portion by this area designation member.Alternatively, the white board portion may be automatically extractedtaking advantage of a difference in brightness since the white board 20is generally white which is brighter than the background portion and hasoften a higher brightness than the background portion. According to thismethod, since the white board portion is normally placed in the centerof the field, the brightness value of the white board portion is setbased on, for example, the pixel data of high brightness in the centerof the field, and an area including only the white board portion can beextracted by comparing this brightness value with the brightness valuein each pixel position (level of the pixel data).

Another method for reducing the coloring phenomenon during the imageprocessing may be as follows. As a γ-characteristic for the blockincluding the white board portion and the background portion,γ-characteristic for a block which is most adjacent to this block anddoes not include both the white board portion and the background portionis used, so as to eliminate the influence of the pixel data of thebackground portion in the illuminance nonuniformity correction.

FIG. 51 is a diagram showing a block construction in which a processingblock for reducing the coloring phenomenon is added to the firstγ-characteristic setting device 324 of the first embodiment. FIG. 51differs from FIG. 15 in that a white saturation level correction device324 h is added between the white saturation level setting device 324 dand the white saturation level interpolation calculator 324 e, and aboundary block extractor 324 g is added between the white saturationlevel correction device 324 h and the histogram generator 324 c.

If a similar modification is introduced to the block diagram of FIG. 38,the first γ-characteristic setting device 324 according to the secondembodiment can also reduce the coloring phenomenon.

In FIG. 51, the boundary block extractor 324 g extracts blocks includingthe white board portion and the background portion based on thehistogram of level-frequency distribution generated for each block. Inother words, the extractor 324 g extracts the blocks whose histogram oflevel-frequency distributions have two convex portions in the white areaas shown in FIG. 49A or 50A, and designates the blocks havingγ-characteristics to be used for these extracted blocks.

The white saturation level correction device 324 h changes the whitesaturation level of each block extracted by the boundary block extractor324 g to that of the block designated by the boundary block extractor324 g. This change is made to use the white saturation level set for theblock which does not include both the white board portion and thebackground portion and is adjacent to the extracted block as the whitesaturation level for the extracted block.

The extraction of the blocks including the white board portion and thebackground portion by the boundary block extractor 324 g is performed asfollows in accordance with a flowchart of FIG. 52.

First, the counter M for counting the block number is set at “1” (Step#150). Since the extraction order of the blocks is along rasterdirection of the block division shown in FIG. 20, M=L·(I−1)+J and theblock B(I, J) corresponds to the block B(L·(I−1)+j).

Subsequently, the level w corresponding to the peak value of the firstconvex portion of the histogram of level-frequency distributiongenerated for the block B(1) is detected. Taking the histogram oflevel-frequency distribution shown in FIG. 48 as an example, the level wcorresponding to the peak value of the convex portion U1 is detected(Step #152). This level w is detected in the similar manner as the levelw used to set the white saturation level W of the γ-characteristic forthe illuminance nonuniformity correction is calculated. Specifically,the most frequent level W of a distribution in a range d lower than themaximum level p is calculated. In FIG. 48, the level p and the range dcorrespond to the maximum level of the pixel data included in the blockB(i) and the range for detecting the level w.

Subsequently, a valley V between the convex portions U1 and U2 isdetected (Step #154). This detection is made by calculating a levelhaving a frequency lower than a predetermined threshold value tnum(e.g., frequency of 20% of a peak value fpnum of the convex portion U1)in a range below the level w and judging whether the calculation resultcontinues a predetermined number of times tt (e.g., 3 to 5) or more. Inthe case that the levels lower than the threshold value tnum continuethe predetermined number of times tt or more, its level range isdetected as a valley V.

It is then judged whether the valley V has been detected (Step #156).Unless the valley V has been detected (NO in Step #156), this routineproceeds to Step #164 in which a flag FLGM(M) is reset to “0”. The flagFLGM(M) indicates the block including the white board portion and thebackground portion.

On the other hand, if the valley V is detected (YES in Step #156), alevel w′ corresponding to the peak value of the second convex portion U2is detected (Step #158). This detection is made by calculating a levelhaving a frequency lower than a predetermined threshold value ynum(e.g., frequency of 30% of a peak value fpnum) in a range below thelevel w and judging whether the calculation result continues apredetermined number of times yt (e.g., 3 to 5) or more. In the casethat the levels lower than the threshold value tnum continue thepredetermined number of times yt or more, its level range is detected asthe second convex portion U2.

It is then judged whether the second convex portion U2 has been detected(Step #160). Upon the detection of the second convex portion U2 (YES inStep #160), the flag FLGM(M) is set at “1” (Step #162). Unless thesecond convex portion U2 has been detected (NO in Step #160), thisroutine proceeds to Step #164, in which the flag FLGM(M) is reset to“0”.

After the count value of the counter M is incremented only by “1” (Step#166), it is judged whether the count value M is larger than the totalblock number N (=k×L) (Step #168). If M≦N (NO in Step #168), thisroutine returns to Step #152 and a processing similar to the above isperformed for the next block B(2) (Steps #152 to #168). Hereafter, thesimilar processing is performed in the similar manner for the respectiveblocks B(M). If M>N (YES in Step #168), the judgment as to whether ornot the block includes the white board portion and the backgroundportion has been made for all blocks. Subsequently, the blocks includingboth the white board portion and the background portion are extracted bychecking the flags FLGM(M) set for the respective blocks (Steps #150 to#180).

This extraction of the blocks is performed as follows. First, thecounter M for counting the block number is set at “1” (Step #170) and itis judged whether the flag FLGM(1) for the block B(1) is set at “1”(Step #172). If the flag FLGM(1) is reset (NO in Step #172), thisroutine proceeds to Step #178.

If the flag FLGM(1) is set at “1” (YES in Step #172), the blocks whichdo not include both the white board portion and the background portionare searched by checking the flags FLGM(I) of the blocks B(I)neighboring the block B(1) (Step #174). This search is performed for 5×5blocks centered on the block B(M) as shown in FIG. 53. The search methodis such that 5×5 block is divided into four small blocks of 3×3 in whichthe block B(M) is located at a lower right corner, an upper left corner,an upper right corer and a lower left corner, respectively, and thesearch is performed for the respective small blocks.

In each small block, the flags FLGM(I) are checked in an order numberedin the blocks of FIGS. 54A to 54D. The block B(I) whose FLGM(I) is firstconfirmed to be “0” is extracted as a block whose γ-characteristicshould be used as that of the block B(M).

In the case of the block B(1), it is located at an upper left corner ofthe picked image. Accordingly, the flags FLGM(I) are checked for theneighboring blocks of the case shown in FIG. 54D. For example, ifFLGM(I)=0 for the first time in the third block (block obliquelydownward from the block B(1) to the left), this block B(I) is extractedas a block whose γ-characteristic should be used as that of the blockB(M).

When the block B(I) is extracted, the position information of this blockB(I) is so stored as to correspond to the block B(I) (Step #176).

Subsequently, after the count value of the counter M is incremented by“1” (Step #178), it is judged whether the count value M is larger thanthe total block number N (Step #180). If M N (NO in Step #180), thisroutine returns to Step #172 and a processing similar to the above isperformed for the next block B(2) (Steps #172 to #180).

Thereafter, the similar processing is performed in the similar mannerfor the respective blocks B(M). If M>N (YES in Step #180), this routineends upon the judgment that the designation of the blocks whosecharacteristic should be used as that of the block including both thewhite board portion and the background portion has been completed forall such blocks.

The blocks extracted by the boundary block extractor 324 g and theinformation on the blocks whose γ-characteristics should be used for theextracted blocks are inputted to the white saturation level correctiondevice 324 h. Out of the white saturation levels set for the respectiveblocks by the white saturation level setting device 324 d, those set forthe blocks including both the white board portion and the backgroundportion are replaced by the white saturation levels set for thedesignated blocks not including both the white board portion and thebackground portion.

As described above, in the first γ-characteristic setting device 324 forreducing the coloring phenomenon, for the blocks including both thewhite board portion and the background portion, the white saturationlevel of the white board portion is not detected based on the histogramof level-frequency distribution of the pixel data included in theseblocks, but the γ-characteristic is set using the white saturation levelof the white board portion detected in the blocks not including both thewhite board portion and the background portion. Accordingly, thecoloring at the boundary portion between the white board portion and thebackground portion caused by the setting of an improper γ-characteristiccan be securely prevented.

In the first γ-characteristic setting device 324 for reducing thecoloring phenomenon, whether or not the block includes both the whiteboard portion and the background portion is detected using the histogramof level-frequency distribution of each block. The boundary positionbetween the white board portion and the background portion can bedetected using the above detection result.

Specifically, since the flag FLGM indicative of the presence or absenceof the boundary between the white board portion and the background isset for each block, the blocks including the boundary between the whiteboard portion and the background portion (hereinafter, “boundaryblocks”) can be extracted by extracting the blocks where FLGM=1.

By connecting the extracted boundary blocks, the shape of the boundaryand the outline of the boundary positions can be known. In the case thata picked image in which a white board image is located in the center isdivided by rectangular blocks, for example, as shown in FIG. 55,boundary blocks including a boundary Z indicated by a sketch in FIG. 55are extracted by extracting the blocks where FLGM=1, and the schematicshape of the boundary Z (laterally long rectangle) can be judged byconnecting the boundary blocks.

If the boundary positions in each boundary block can be presumed pixelby pixel, the boundary positions in the field, i.e., the area of thewhite board image can be accurately known. If the γ-characteristic isdiffered in the white board portion and the background portion, a moresuitable image for the character representation in the white board imagecan be obtained even if the background image is included in the field.Further, in the case that the contrast between the base portion (whiteportion) and the character portion is made clear by applying a binaryprocessing to the picked image, a suitable binary processing can beperformed by changing a binary threshold value in the white boardportion and the background portion.

Next, a method for presuming the boundary positions in each boundaryblock pixel by pixel is described.

In the case that the image in the block is mostly constituted by thewhite image of the white board portion and the white image of thebackground portion (having a lower brightness than the white boardportion) and there is a fixed difference in brightness between the whiteboard portion and the background portion, the level distribution is atwo-peak distribution having a convex portion U1 corresponding to thewhite board portion and a convex portion U2 corresponding to thebackground portion as shown in FIG. 56. The convex portions U1, U2 arerelatively pointed.

In such a case, since the pixel data of the white board portion in theblock gather around the convex portion U1 and those of the backgroundportion gather around the convex portion U2, the domain of brightness isdivided into ranges A1, A2 above and below a valley value t1 between theconvex portions U1 and U2. Assuming a1, a2 denote frequencies includedin the respective ranges A1, A2, a ratio of a1 to a2 approximates to aratio of S1 (area of the white board portion in the block) to S2 (areaof the background portion in the block).

If the histogram of level-frequency distribution generated, for example,for the boundary block B1 including the transversely extending boundaryZ in FIG. 55 is assumed to be the one of FIG. 56, since the boundary Zis substantially horizontal in the boundary block B1, the boundary Z ispresumed to be located in a position where the boundary block B1 isdivided at a1:a2 along vertical direction. The boundary position in theboundary block B2 can be presumed according to a similar method.

Accordingly, if the frequency ratios a1:a2 are compared to besubstantially or about the same between the neighboring boundary blocksB1 along horizontal direction, these blocks B1 are presumed to be blocksincluding only the horizontal portion of the boundary Z. Likewise, ifthe frequency ratios a1′:a2′ are compared to be substantially or aboutthe same between the neighboring boundary blocks B2 along verticaldirection, these blocks B2 are presumed to be blocks including only thevertical portion of the boundary Z.

On the other hand, in the blocks B3 including the corners of the whiteboard image, frequency ratio a1″:a2″ is absolutely different from thefrequency ratio a1:a2 of the blocks B1 neighboring along horizontaldirection and the frequency ratio a1′:a2′ of the boundary blocks B2neighboring along vertical direction. Accordingly, the blocks B3 havingsuch a frequency ratio a1″:a2″ are presumed to be blocks at the cornersof the white board image. As shown in FIG. 47, the boundary Z ispresumed to be located in a position where the blocks B3 are divided inL-shape using the frequency ratio a1:a2 of the blocks B1 neighboringalong horizontal direction and the frequency ratio a1′:a2′ of theboundary blocks B2 neighboring along vertical direction.

Since the blocks B3 including the corners of the white board image canbe judged based on the connected state of the boundary blocks, theposition of the boundary Z in the blocks B3 may be presumed by dividingthem in L-shape using the frequency ratio a1:a2 of the blocks B1neighboring along horizontal direction and the frequency ratio a1′:a2′of the boundary blocks B2 neighboring along vertical direction.

According to the method for detecting the white level of the white board20 based on the histogram of level-frequency distribution of the pixeldata, it is difficult to accurately detect it also in the case wherematerials of intermediate gradation such as pictures or graphs areadhered to the white board 20.

This is because of the following reason. In the case that the image inthe block has intermediate gradation such as a picture, most pixel dataspread in the gray area. Accordingly, a convex portion U correspondingto the white portion and a convex portion C corresponding to thecharacter portion cannot be clearly seen in the histogram oflevel-frequency distribution set for this block as shown in FIG. 57.Thus, even if the method for detecting the level w corresponding to thepeak value of the convex portion U of the white portion of the histogramof level-frequency distribution shown in FIG. 19 is applied to the blockhaving the histogram of level-frequency distribution shown in FIG. 57,the level w can be neither accurately nor securely detected.

On the other hand, if a γ-correction similar to a binary processing isapplied in the block including an image of intermediate gradation suchas a picture, the image quality of the picture or the like is reduced,making it an unnatural image. Thus, it is desirable to perform aγ-correction similar to the one for natural images for this block.

Accordingly, the blocks having an image of intermediate gradation areextracted based on the shape of the histogram of level-frequencydistributions generated for the respective blocks, and a γ-correction isperformed for the extracted blocks using a predeterminedγ-characteristic for intermediate gradation (e.g., γ-characteristic usedin the first γ-correction device).

The following two methods can be adopted to judge whether the blockincludes an image of intermediate gradation based on the shape of thehistogram of level-frequency distribution.

The first method is applied in the case that a maximum frequency fp ofthe histogram of level-frequency distribution is lower than apredetermined threshold value thd and the convex portions of thehistogram of level-frequency distribution are flat. Dispersion iscalculated for a distribution within a predetermined range bd below alevel w having the maximum frequency fp, and the judgment is made bycomparing the calculation result with the predetermined threshold valuethb. Only the pixel data in the range bd are used in the calculation ofdispersion to reduce the influence of the pixel data corresponding tothe character representation. It should be noted that the thresholdvalue thb is a threshold value of dispersion which can be presumed to bein the white board portion and is empirically obtained in advance.

Accordingly, if the calculated dispersion is larger than thepredetermined threshold value thb, the image in the block is judged notto be an image of the white board portion.

The second method is applied in the case that a variation of thehistogram of level-frequency distribution is relatively large. In arange below a level w having a maximum frequency fp, a level ph having afrequency lower than Z % (e.g., 50%) of the maximum frequency fp andclosest to the level w is calculated. The judgment is made by comparinga difference Δw(=w−ph) between the level ph and the level w with apredetermined threshold value thph. It should be noted that thepredetermined threshold value thph is a threshold value of the leveldifference which can be presumed to be the white board portion and isempirically obtained in advance.

Accordingly, when the calculated level difference Δw is larger than thepredetermined threshold value thph, the image in this block is judgednot to be an image of the white board portion.

In the first and second embodiments, the γ-correction is applied to theimage after the illuminance nonuniformity correction using theγ-characteristic for the black intensification whose black saturationlevel B is variably set by the black density adjustment switch 18.However, the γ-correction for the black intensification may be performedas follows without using the γ-characteristic for the blackintensification. After such a γ-correction as to make the base portionof the picked image white is performed using the γ-characteristic forthe illuminance nonuniformity correction, a minimum level h′ of thepixel data is calculated, and the γ-correction is performed using aγ-characteristic for level-converting the pixel data level between theminimum level h′ and the white saturation level w by 256 gradationlevels.

Specifically, if a histogram of level-frequency distribution as shown inFIG. 58A is obtained for the image after the illuminance nonuniformitycorrection, a level h′ having a lowest brightness of the black area iscalculated from this histogram of level-frequency distribution, and aγ-characteristic shown in FIG. 58B is set using this level h′ and thewhite saturation level w. The γ-correction may be applied to the imageafter the illuminance nonuniformity correction using thisγ-characteristic. According to this method, since the γ-correction is soperformed as to extend the brightness range of the image after theilluminance nonuniformity correction to a range of 256 gradation levels,the dynamic range is extended and the quality of the picked image can beimproved.

FIG. 59 is a block construction diagram of the electronic camera 1according to a third embodiment; FIG. 60 is a detailed block diagram ofa construction for applying an image processing to a color image fromthe A/D converter 320 to the first and second γ-correction devices 326,327; and FIG. 61 is a block diagram showing the internal construction ofthe first γ-characteristic setting device 324 according to the thirdembodiment.

The electronic camera 1 of the third embodiment is provided with afunction of preventing an occurrence of an undesired event where acharacter representation having become unclear due to the regularreflection of the illumination light (including both natural light andflash light) becomes even more unclear when the illuminancenonuniformity correction is applied to a picked image including a lightimage regularly reflected by an object. Since this function concerns theilluminance nonuniformity correcting function, but not the oblique imagecorrecting function, the elements relating to the oblique imagecorrecting function are deleted from FIGS. 59 to 61 in order tosimplified the description.

The method according to the third embodiment for the illuminancenonuniformity correction is basically same as the one described in thefirst embodiment. Accordingly, description is supplementarily given onthe construction relating to a newly added function in the descriptionbelow.

The block construction diagram shown in FIG. 56 differs from the oneshown in FIG. 36 in that the oblique image correction device 321 and themode setting switch 16 are deleted and a warning buzzer 23 and a regularreflection warning switch 24 are added. Since the oblique imagecorrecting function is deleted in the electronic camera 1 according tothe third embodiment, the oblique image correction device 321 and themode setting switch 16 which relate to this function are deleted fromthe block construction of FIG. 59.

In FIG. 59, the switch circuit 328 switches the connection of the imagememory 323 with the first and second γ-correction devices 326, 327, andthe switch circuit 329 switches the connection of the first and secondγ-correction devices 326, 327 with the HD card 13. The switching of theswitch circuits 328, 329 is controlled in accordance with a controlsignal outputted from the CPU 30 in conformity with the set state of theilluminance nonuniformity correction switch 17. If the illuminancenonuniformity correction switch 17 is set “OFF” (if the natural imagemode is set), the image memory 323 and the first γ-correction device 326are connected and the first γ-correction device 326 and the HD card 13are connected. If the illuminance nonuniformity correction switch 17 isset “ON” (if the character image mode is set), the image memory 323 andthe second γ-correction device 327 are connected and the secondγ-correction device 327 and the HD card 13 are connected.

Further, the buzzer 23 is provided at an upper right corner of the rearsurface of the electronic camera 1 as shown in FIG. 62 and is adapted tonotify an image capture person that, when a character image drawn on thewhite board 20 is captured, it becomes unclear due to the regularreflection of the illumination light by the white board 20. Hereinafter,this warning is referred to as a “regular reflection warning”.

The regular reflection warning switch 24 is provided at the right sideof the black density adjustment switch 18 on the rear surface of theelectronic camera 1 as shown in FIG. 62 and is adapted to designate theregular reflection warning. The regular reflection warning switch 24 isan ON/OFF switch whose operation button is slidable along transversedirection. If the “regular reflection warning” is designated by theregular reflection warning switch 24, a captured image is divided into aplurality of blocks (small images) and the presence of the regularlyreflected light is judged for each block using the histogram oflevel-frequency distribution of the pixel data included in the block. Awarning sound is given from the buzzer 23 if the regularly reflectedlight is detected in any of the blocks. The electronic camera 1 alsowarns the image capture person of a possibility that the quality of thecaptured image is reduced due to the regularly reflected light byturning a LED indicator 25 for the regular reflection warning providedin the viewfinder frame 42 as shown in FIG. 63. On the other hand, whenthe regular reflection warning switch 24 is “OFF”, neither the detectionof the regularly reflected light nor the regular reflection warning ismade.

The choice as to whether the regular reflection warning is to be givenis left to the image capture person as described above for the followingreason. The regularly reflected light is problematic in the imagecapturing operation when the character image mode is set. Conversely,the regularly reflected light may be effectively utilized as an imagecapturing effect in the natural image mode where image capturing similarto usual picture taking is performed. Accordingly, the regularreflection warning can be made if necessary according to the imagecapturing purpose, scene, etc. Thus, the regular reflection warning maybe constantly made without providing the regular reflection warningswitch 24.

The block diagram shown in FIG. 60 differs from that shown in FIG. 37only in that the first γ-characteristic setting device 324B for greencomponents judges whether the captured image includes an image of theregularly reflected illumination light and this judgment result isoutputted as a detection information of the regularly reflected light.Further, the block construction shown in FIG. 61 differs from the oneshown in FIG. 15 in that a regular reflection detector 324 i is added.The detector 324 i judges whether the captured image includes an imageof the illumination light regularly reflected block by block when theregular reflection warning is designated by the regular reflectionwarning switch 24, thereby detecting the captured image including theimage of the regularly reflected light. The detector 324 i judgeswhether the image of the regularly reflected light is included in eachblock B(I, J) based on the shape of the histogram of level-frequencydistribution generated for each block.

Specifically, if the illumination light such as ceiling light andsunlight coming through the windows is regularly reflected by the whiteboard 20 when a character representation such as characters and figuresdrawn on the white board 20 is captured, the pixel data of saturationlevel are outputted from the pixels having received the regularlyreflected light. Accordingly, most of the pixel data constituting theimage of the white board 20 are pixel data of saturation level in theblocks including the image of the regularly reflected light. Thus, thehistogram of level-frequency distribution for such a block is shapedsuch that a level w having a maximum frequency of a convex portion Ucorresponding to the white board 20 substantially agrees with a maximumlevel p.

The regular reflection detector 324 i calculates the level w having themaximum frequency of the convex portion U of the histogram oflevel-frequency distribution corresponding to the white board 20according to a method similar to the method for setting the whitesaturation level W of the γ-characteristic for the illuminancenonuniformity correction and compares this calculation result with themaximum level p. If the level w substantially agrees with the maximumlevel p, the detector 324 i judges that the image of the regularlyreflected light is included in this block and outputs this judgmentresult to the CPU 30.

The CPU 30 causes the buzzer 23 to give out a sound in accordance withthe judgment result of the regular reflection detector 324 i and turnsthe LED indicator 25 on to give an image capture person a warning thatthe captured image includes the regularly reflected light.

The first γ-characteristic setting devices 324A, 324B for red and bluecomponents have the same internal construction as the firstγ-characteristic setting device 324B for green components except theregular reflection detector 324 i.

Next, an image capturing control of the electronic camera 1 according tothe third embodiment is described with reference to a flowchart of FIGS.65 to 68. It is assumed that the image capturing/reproduction switch 12is set at the image capturing side. When the electronic camera 1 isactivated and the ST1 switch is turned on by the shutter release button10, an object image is picked up by the CCD 22 and an image processingis applied to the picked image in a specified cycle. When the switch S 2is turned on, the image picked up after this is stored in the HD card 13after a specified image processing is applied thereto.

When the main switch 14 is turned on to activate the electronic camera1, the image capturing operation is enabled. If the zoom switch 11 isoperated in this state (YES in Step #200), the zoom lens of the takinglens 2 is driven according to the operated direction and the operatedamount to change a zooming ratio (Step #202). Thereafter, when the ST1switch is turned on by partly pressing the shutter release button 10(YES in Step #204), the image capturing preparation processing isperformed in Step #206.

Specifically, an object distance D_(A) is first detected by the lightmeter 41 (Step #206). The light meter 41 emits infrared rays for thelight metering toward an object through the light emitting portion 411and picks up a light meter data by receiving the light reflected by theobject by the light receiving portion 412, and calculates the distanceDA from the object to the sensing surface in the center of the fieldusing the picked data. Then, a lens drive amount by which the takinglens 2 is driven to attain an in-focus condition is calculated based onthe calculated object distance D_(A) (Step #208).

Subsequently, it is judged whether the regular reflection warning hasbeen designated by the regular reflection warning switch 24 (Step #210).A regular reflection warning processing is performed in Steps #212 to#218 if the regular reflection warning has been designated (YES in Step#210), whereas it is not performed by skipping Steps #212 to #218 unlessotherwise (NO in Step #210).

In the regular reflection warning processing, an image capturingmagnification m_(A) (=a f/DA, a: proportion coefficient) in the centerof the field is calculated based on the object distance D_(A) and afocal length f of the taking lens 2 (Step #212). Whether the image ofthe regularly reflected light is included in the captured image is thendetected in accordance with a subroutine “Regular Reflection Detection”shown in FIG. 68 (Step #214).

The detection as to whether the image of the regularly reflected lightis included in the captured image is made as follows. First, a blocksize S0 (=S0·m_(A)/m0) for dividing the picked image is calculated usingthe image capturing magnification m_(A), a predetermined reference imagecapturing magnification m0 and a block size S0 (Step #260). Further, ablock number n is calculated based on the block size S and the size ofthe sensing surface (Step #262).

Subsequently, the counter M for counting the block number n is set at“1” (Step #264). Since the order of the blocks in the γ-characteristicsetting is along raster direction in the block division shown in FIG.20, M=L·(I−1)+J. Thus, the block B(I, J) corresponds to the blockB(L·(I−1)+J).

All pixel data included in the block B(M) are read (Step #266), and ahistogram of level-frequency distribution as shown in FIG. 23 or 64 isgenerated using the pixel data except X % of pixel data at the highlevel side (Step #268). Then, the level w corresponding to the peakvalue of the convex portion U corresponding to the white portion of thehistogram of level-frequency distribution is calculated (Step #270) andit is judged whether this level w substantially agrees with the maximumlevel p (=255) of the histogram of level-frequency distribution (Step#272).

If the level w substantially agrees with the maximum level p (YES inStep #272), it is judged that the image of the regularly reflected lightis included in the block and a flag FLAGH is set at “1” (Step #280) andthis subroutine returns. The FLAGH is a detection flag of the regularlyreflected light and indicates that an image of the regularly reflectedimage is included in a captured image when it is set at “1” whileindicating that no image of the regularly reflected light is included ina captured image when it is reset at “0”.

Unless the level w substantially agrees with the maximum level p in Step#272, the count value of the counter M is incremented by “1” (Step#274). Thereafter, it is judged whether the count value M is larger thanthe total block number n (Step#276). If M≦−n (NO in Step #276), thissubroutine returns to Step #266 to judge whether an image of theregularly reflected light is included in the next block B(M) (Steps #266to #272).

If the image of the regularly reflected light has been detected in noneof the blocks B(M) (YES in Step #276), it is judged that no image of theregularly reflected light is included in the captured image and thissubroutine returns after the flag FLAGH is reset to “0” (Step #278).

Referring back to FIG. 65, upon the completion of the regularlyreflected light detection, the presence or absence of the image of theregularly reflected light is judged based on the state of the flag FLAGH(Step #216). If the flag FLAGH is set at “1” (the image of the regularlyreflected light is present) (YES in Step #216), the regular reflectionwarning is made by the buzzer 23 and the LED indicator 25 (Step #218).On the other hand, if the flag FLAGH is reset at “0” (the image of theregularly reflected light is absent) (NO in Step #216), Step #218 isskipped, so that the regular reflection warning by the buzzer 23 and theLED indicator 25 is not made.

Subsequently, a data on the object brightness (light meter data) isobtained by the light meter 40 (Step #220), and the exposure controlvalues are calculated based on this light meter data (Step #222). It isthen judged whether the illuminance nonuniformity correction has beendesignated by the illuminance nonuniformity correction switch 17 (Step#224 in FIG. 66). If the illuminance nonuniformity correction has beendesignated (YES in Step #224), a control signal representing theprohibition of the firing is outputted to the emission controller 34 toprohibit the flash 7 from firing (Step #226). Unless the illuminancenonuniformity correction has been designated (NO in Step #222), Step#226 is skipped, so that the firing of the flash 7 is not prohibited. Inthis way, the image capturing preparation processing is completed andthe electronic camera 1 waits on standby for an exposure.

The firing of the flash 7 is prohibited when the illuminancenonuniformity correction is designated in order to avoid the followingimage capturing error. In the case that the flash 7 is, for example,automatically fired in a scene where the white board 20 is captured fromfront, characters in the picked image may be unreadable due to the flashlight fully reflected by the white board 20.

When the shutter release button 10 is fully pressed to turn the ST2switch on in the exposure standby state (YES in Step #228), this routineproceeds to Step #232 to start the exposure. On the other hand, if theshutter release button 10 is kept partly pressed, i.e., the ST1 switchis still on (YES in Step #230), this routine returns to Step #206 torepeat the aforementioned image capturing preparation processing (a loopof Steps #206 to #230). If the shutter release button 10 is released tothereby turn the ST1 switch off (NO in Step #230), this routine returnsto Step #200.

Upon the start of the exposure, after the data on the lens drive amountis outputted to the lens driver 37 and the taking lens 2 is focused(Step #232), the aperture value data Av of the exposure control valuesis outputted to the diaphragm driver 39 to adjust the aperture of thediaphragm 21 (Step #234).

It is then judged whether the illuminance nonuniformity correction hasbeen designated (Step #236). If the illuminance nonuniformity correctionhas been designated (YES in Step #236), the block size S used to dividethe image into a plurality of blocks is calculated (Step #238). Thiscalculation is made according to a method similar to the one adopted inStep #260 during the regularly reflected light detection processing.

When the setting of the block size is completed, the shutter speed datacalculated in Step #222 is outputted to the CCD driver 31 to start animage pickup operation (integration) by the CCD 22 (Step #240). The CCD22 picks up an object image by storing electric charges (electric chargeintegration) in a photosensitive portion thereof for a predeterminedtime after the electric charges in the photosensitive portion are resetin accordance with a drive control signal from the CCD driver 31.

Upon the completion of the image pickup operation by the CCD 22, thereading of the electric charges (pixel data) stored in the respectivepixels of the photosensitive portion is started (Step #242 in FIG. 67).The pixel data of the CCD 22 are successively read in arrow directionevery vertical line as shown in FIG. 33 and inputted to the imageprocessor 32. The pixel signals inputted to the image processor 32 arestored in the image memory 323 after being converted into pixel data inthe A/D converter 320, and are inputted to the first γ-characteristicsetting device 324.

Subsequently, it is judged whether the illuminance nonuniformitycorrection has been designated (Step #244). If the illuminancenonuniformity correction has been designated (YES in Step #244), thefirst γ-characteristic setting device 324 sets a γ-characteristic forthe illuminance nonuniformity correction for each block in accordancewith the subroutine “γ-Characteristic Setting” shown in FIG. 32 (Step#246). Here, no description is given on the setting of theγ-characteristic since it is identical to the aforementioned processing.

Subsequently, the white saturation level W(I) of the γ-characteristicfor the illuminance nonuniformity correction set for each block B(I) isinterpolated to set γ-characteristics for the illuminance nonuniformitycorrection in pixel positions other than the center position of eachblock B(I) (Step #248). While the set γ-characteristics are inputted tothe second γ-correction device 327, the pixel data are transferred fromthe image memory 323 to the second γ-correction device 327 via theswitch circuit 328. After the γ-correction is applied to the pixel datausing the γ-characteristic for the illuminance nonuniformity correctioncorresponding to that pixel position, the γ-correction is performedusing the γ-characteristic for the black intensification (Step #250).

On the other hand, if the illuminance nonuniformity correction has notbeen designated (NO in Step #244), the pixel data are transferred fromthe image memory 323 to the first γ-correction device 326 via the switchcircuit 328 and the γ-correction is applied to the pixel data using theγ-characteristic after the γ-correction are written in the HD card 13via the switch circuit 329 (Step #254).

The pixel data after the γ-correction are successively written in the HDcard 13 via the switch circuit 329 (a loop of Steps #244 to #256). Uponthe completion of the writing of all pixel data in the HD card 13 (YESin Step #256), a control signal representative of the completion of thereading of the pixel data is outputted to the CCD driver 31 and acontrol signal representative of the completion of the writing of thepixel data is outputted to the card driver 33, thereby completing oneimage pickup operation (Step #258). Then, this routine returns to Step#200 for the next image capturing operation.

As described above, during the image capturing preparation processing,the picked image is divided into a plurality of blocks; and theregularly reflected light is detected by judging every block whether theimage of the light regularly reflected by the object (white board 20) isincluded in the block using the histogram of level-frequencydistribution generated every block. Accordingly, even a spot regularlyreflected light can be securely detected. Since the regular reflectionwarning is given to the image capture person based on the detectionresult, in the case that an object is characters and/or figures drawn onthe white board 20 and such a representation becomes unclear due to theregular reflection of the illumination light by the white board 20, anerroneous operation of image capturing an image having a lowrepresentation value can be prevented by the regular reflection warning.

Although only the regular reflection warning is made upon the detectionof the regularly reflected light in the foregoing embodiments, thestorage of the captured image in the HD card 13 may be prohibited inaddition to the regular reflection warning in order to effectively usethe memory capacity of the HD card 13 since the image representing thecharacter image having become unclear due to the regular reflection ofthe illumination light has a low representation value. In such a case,as shown in FIG. 69, Step #231 of judging the set state of the flagFLAGH (judgment as to the presence or absence of the image of theregularly reflected light corresponding to Step #216) is inserted, forexample, between Steps 228 and 232 in the flowchart of FIG. 66. If theflag FLAGH is set at “1” (YES in Step #231), this routine returns toStep #206 to perform the image capturing preparation processing. If theflag FLAGH is reset at “0” (NO in Step #231), this routine proceeds toStep #232. In other words, unless the flag FLAGH is reset at “0”, theimage capturing preparation processing may be repeated regardless ofwhether the ST2 switch is on or not.

In the foregoing embodiments, when the shutter release button 10 isfully pressed, a specified image processing corresponding to thedesignation by the illuminance nonuniformity correction switch 17(illuminance nonuniformity correction) is applied to the picked imageregardless of whether the regular reflection warning has been given ornot and, then, the image data is stored in the HD card 13. However, whenthe regular reflection warning is given, an image processing for theusual image capturing operation is applied to the picked image (i.e., noilluminance nonuniformity correction is performed) regardless of the setstate of the illuminance nonuniformity correction switch 17 and, then,the image data is stored in the HD card 13.

In this case, as shown in FIG. 70, Steps #235 and #243 of judging thepresence or absence of the image of the regularly reflected light basedon the state of the flag FLAGH is inserted between Steps #234 and #236and between Steps #242 and #244 in the flowchart of FIGS. 66 and 67. Ifthe flag FLAGH is set at “1” in Step #235 (YES in Step #235), Steps#236, #238 are skipped. If the flag FLAGH is set at “1” in Step #243(YES in Step #243), this routine proceeds to Step #252.

As described above, when the image of regularly reflected light isincluded in the captured image, the image processing is performed byapplying the γ-correction for the usual image capturing operation evenif the illuminance nonuniformity correction has been designated. Thisprevents a problem that the character representation having becomeunclear due to the regularly reflected light becomes even more uncleardue to the illuminance nonuniformity correction, thereby furtherreducing the image quality and representation value.

Although the present invention has been fully described by way ofexample with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless otherwise such changes andmodifications depart from the scope of the present invention, theyshould be construed as being included therein.

1-41. (Cancelled)
 42. An image capturing apparatus comprising: a colorimage pickup device which photoelectrically picks up a light image of anobject to generate image data of three primary color components; a whitelevel calculator which calculates a white level for an image of eachcolor component based on image data of its color component; aγ-characteristic setter which sets a γ-characteristic for an image ofeach color component to convert image data of its color component abovethe calculated corresponding white level to a white saturation level;and a γ-characteristic corrector which corrects image data of each colorcomponent in accordance with the set γ-characteristic. 43-58.(Cancelled)
 59. A method for processing image data of three primarycolor components generated by a color image pickup device, the methodcomprising the steps of: calculating a white level for an image of eachcolor component based on image data of its color component; setting aγ-characteristic for an image of each color component to convert imagedata of its color component above the calculated corresponding whitelevel to a white saturation level; and correcting image data of eachcomponent in accordance with the set γ-characteristic. 60-63.(Cancelled)